This is s seven part answer.
I suggest that you make your land mass long and narrow and extend almost directly north and south.
And also make your planet as small as possible consistent with having a breathable atmosphere.
And maybe make the planet have a greater axial tilt than the Earth does.
You can also make different parts of your land mass have different climates due to different altitudes.
You can also use warm and cold sea currents to heat and cool different parts of your land mass.
Part One: Stretch the Land Mass North and South.
Earth has a polar radius of 6,356.8 kilometers or 3,949.9 miles. It thus has a polar circumference of about 39,940.9 kilometers or 24,817.932 miles. The distance from the equator to the North Pole or South Pole is thus a quarter of its polar circumference, or 9,985.22 kilometers, or 6,204.483 miles.
On the planet Earth extending a landmass 9,985.22 kilometers, or 6,204.483 miles, from the equator to one of the poles will put different parts of the landmass in every climate zone which depends on latitude. Other factors may influence how wet or dry various parts of the landmass are.
The size of the land mass is specified as 250,000 square kilometers. Assuming that it is an artificial perfect north-south rectangle it would be 25.037 kilometers or 15.557 miles wide.
But on Earth a landmass which extends from the tropic zone to the polar zone only has to extend through the entire temperate zone and a little bit more more both north and south. It might stretch from a little bit closer to the Equator than the Tropic of Cancer or the Tropic of Capricorn to a little bit farther than the Arctic Circle or the Antarctic circle to have small regions in the tropical zone and in the polar zone, while most of it will have various temperate climates.
On Earth the Tropic of Cancer and the Tropic of Capricorn are 23.43661 degrees of latitude from the Equator, and the Arctic Circle and the Antarctic circle are about 66.5 degrees from the equator. So the separation between the Tropic of Cancer and the Arctic circle is about 43.1 degrees of latitude.
Assuming that your continent is an artificial rectangle oriented north-south with 10 percent above the Arctic Circle and 10 percent below the Tropic of Cancer, it would extend over a total of 53.875 degrees of Latitude, which is 0.1496 of the full polar circumference of Earth. Since the polar circumference of Earth is 39,940.9 kilometers, if your landmass was an artificial perfect north-south rectangle it would extend for about 5,983.2496 kilometers north to south, and if it had a total area of 250,000 square kilometers it would be 41.7833 kilometers or 25.9629 miles wide.
Part two: Shrink the Planet.
On a smaller but still habitable planet, your land mass could extend to a lesser north-south distance while stretching between the equivalents of the Tropic of Cancer and the Arctic Circle. So how small could a planet be to be able to retain a breathable atmosphere for humans or for intelligent beings with similar environmental requirements.
Well, we should look at what Habitable Planets for Man, Stephen H. Dole, 1964, 2007, has to say.
On page 53 Dole calculates the mass, size, etc. of a planet with a surface gravity of 1.5 times that of Earth, 1.5 g, considering that to be the upper limit of a planet habitable for humans. On page 54 Dole calculates the lower limit of a planet with an atmosphere with enough oxygen for humans.
To prevent atomic oxygen from escaping rapidly from the upper layers of its atmosphere, the planet's escape velocity must be of the order of five times the root-mean-square velocity of the oxygen atoms in the exosphere...
.., then the escape velocity of the smallest planet capable of retaining atomic oxygen may be as low as 6.25 kilometers per second (5 x 1.25). Going back to figure 9, this may be seen to correspond to a planet having a mass of 0.195 Earth mass, a radius of 0.63 Earth radius, and a surface gravity of 0.49 g. Under the above assumptions, such a planet could theoretically hold an oxygen-rich atmosphere, but it would probably be much too small to produce one, as will be shown below.
Dole then discusses the minimum size planet necessary to produce an oxygen-rich atmosphere. He calculates two different minimum sizes, one of 0.25 Earth mass, and one of 0.57 Earth mass, and decides that the first one is too small and the second too large.
...With 0.25 being too low and o.57 being too high, the appropriate mass for the smallest habitable planet must be between these figures, somewhere in the vicinity of 0.4 Earth mass.
Since it is not possible to obtain a more precise determination of the minimum mass of a habitable planet, for our purposes the value of 0.4 Earth mass will be adopted as the lower limit of mass. This corresponds to a planet having a radius of 0.78 Earth radius and a surface gravity of 0.68 g.
So on a planet with a radius of 0.78 Earth radius a land mass stretching 53.875 degrees from north to south would have a length of 4,666.9346 kilometers. If it was an artificial perfect rectangle it would have an east west width of 53.5683 kilometers or 33.2858 miles.
But maybe Dole was wrong, maybe a planet with less than 0.4 Earth mass can produce an oxygen rich atmosphere, possibly even a planet with only 0.195 Earth mass, which should be enough mass to retain an oxygen rich atmosphere. Or possibly an advanced civilization has terraformed that planet in the past, giving it an oxygen rich atmosphere.
So on a planet with mass of 0.195 Earth mass and a radius of 0.63 Earth radius a land mass stretching 53.875 degrees from north to south would have a length of 3,769.4472 kilometers. If it was an artificial perfect rectangle it would have an east west width of 66.3227 kilometers or 41.2110 miles.
I once read, in a novel by Arthur C. Clarke, possibly in collaboration with another writer, a mention that the Moon had been given an Earth like atmosphere. That atmosphere was retained by a layer of nanobots which held on to each other and bounced back any air particles on escape vectors.
If that or some other method of retaining an artificial atmosphere is possible, your planet could be a tiny planet that was once terraformed to be habitable and settled with people, who have reverted to a less advanced state. We can hope they will rebuild their civilization before any action on their part is needed to maintain the habitability of their world.
Thus if your planet is much smaller than 0.195 Earth mass, and its atmosphere is artificially produced and retained, your land mass could be even less than 3,769.4472 kilometers from north to south to reach all the climate zones and thus could be even more than 66.3227 kilometers from east to west.
Part Three: Increase the Axial Tilt of the Planet.
In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane.1 It differs from orbital inclination.
At an obliquity of 0 degrees, the two axes point in the same direction; i.e., the rotational axis is perpendicular to the orbital plane. Earth's obliquity oscillates between 22.1 and 24.5 degrees2 on a 41,000-year cycle. Based on a continuously updated formula, Earth's mean obliquity is currently 23°26′11.8″ (or 23.43661°) and decreasing.
So Earth's axial tilt is about 23.5 degrees, and the Tropics of Cancer and Capricorn are about 23.5 degrees from the Equator, and the Arctic and Antarctic Circles are about 23.5 degrees from the North and South Poles.
So if Earth had an axial tilt of 30 degrees, the temperate zones between the tropics and the polar circles would be only 30 degrees wide.
So if Earth had an axial tilt of 33.25 degrees, the temperate zones between the tropics and the polar circles would be only 23.5 degrees wide.
So if Earth had an axial tilt of 35 degrees, the temperate zones between the tropics and the polar circles would be only 20 degrees wide.
So if Earth had an axial tilt of 40 degrees, the temperate zones between the tropics and the polar circles would be only 10 degrees wide.
In our solar system, the axial tilts of various planets and a couple of other bodies vary between 0.03 degrees for Mercury and 82.23 degrees for Uranus. So it would certainly be possible for your planet to have a larger axial tilt than Earth does.
Part Four: Stretch You Land Mass North to South, and Shrink Your Planet, and Give Your Planet a Larger Axial Tilt.
Combining all three methods of getting your land mass to include all the latitude based climate zones will produce a land mass that is elongated north and south but maybe not too much to be believable. And multiplying its surface area of 250,000 square kilometers a few times would help keep it's elongated shape within plausibility.
Part Five: Climate Zones based on Altitude.
You may have heard of the Hemingway story "The Snows of Kilmanjaro" and the 1952 movie based on it. And here is a link to a photo showing Kilmanjaro and some of that snow.
Mount Kilmanjaro is only 03°04′33″ south of the Equator, but it has snows at the top.
Here is a list of the climate zones of Mount Kilmanjaro:
Bushland / Lower Slope:, 800 m – 1,800 m (2,600 ft – 5,900 ft);
Rainforest Zone: 1,800 m – 2,800 m (5,900 ft – 9,200 ft);
Heather / Moorland: 2,800 m – 4,000 m (9,200 ft – 13,100 ft);
Alpine Desert Zone: 4,000 m – 5,000 m (13,100 ft– 16,400 ft);
Arctic Zone: 5,000 m – 5,895 m (16,400 ft – 19,300 ft).
And here is a link to a picture of Mount Chimborazo, whose peak is the point on Earth farthest from the center of the Earth.
What country is Chimborazo in? Ecuador, a country named after the Equator. Chimborazo is only 01 degrees, 28 minutes, 09 seconds south of the Equator.
At high enough altitudes, places can be snow covered all year even at the equator.
So possibly your land mass doesn't have to stretch a long way from north to south to have many different climates. It might be in the tropics but have high mountains and high plateaus so that some high parts have snow all year just a few miles from lush tropical vegetation at the sea side.
And if prevailing winds dump a lot of moisture on one side the land mass, large parts of the other side might be in the rain shadows of mountains and plateaus and be cold, temperate, and hot deserts without much or any rainfall.
Part Six: Climate Zones Based on Sea Currents.
Other answers have already pointed out examples of lands such as Britain that are warmed by having warm waters flow from the tropics to their shows in currents like the Gulf Stream.
Assume that your land mass is mostly or all in a temperate zone. So the waters around it normally have the same temperatutes as other ocean waters in the temperate zone.
But a large warm current like the Gulf stream comes from closer to the Equator and reaches the southwestern corner of the land mass and warms it significantly. A large island to the west of the land mass block the warm current and prevents it from going north, so the seas northwest of that island are the normal temperatures for that latitude.
But a large cold current like the Labrador Current comes from the Arctic and reaches the northeastern corner of the land mass and cools it significantly. A large island to the east of the land mass block the warm current and prevents it from going north, so the seas southeast of that island are the normal temperatures for that latitude.
So the ocean waters northwest and southeast of the land mass are the same temperatures as other waters in that latitude, but the southwestern waters are much warmer, and the northeastern waters are much colder, and the temperatures of those water bodies affect the temperature of the land mass, especially if if is a long narrow land mass.
Or if it is in the southern hemisphere the warm current could come from the north and the cold current from the south.
And of course the different altitudes of the different parts of the land mass will affect their climates.
Part Seven: Conclusion.
So the ways you can make a land mass as small as Great Britain have diverse climates include making it stretch a long way north and south, making the planet it is on smaller than Earth, making its planet have a larger axial tilt than Earth, giving the land mass a high range of altitudes, and having the land mass reached by warm and by cold currents.