Sauron is thousands of years old. He spent much of that time fighting the Noldor, and other elves. A Noldor army of the size you describe would easily defeat any similar size army of Men, were they so inclined to do so.
Consider:
They survived the breaking of the world.
They fought in total darkness before the making of the Sun and the Moon.
They had millennia of experience to draw from.
Although they prefer more pastoral settings, we can't forget at the skill they had as artificers, enough to kill most of the dragons, drive away the Balrogs, etc.
And yet, they were ultimately not successful. The dragons were slain, the Balrogs driven into hiding, but the Orcs were able to successfully combat them. They have the physical capability to go toe to toe with Elves, and because of their lifespan, the numbers to overwhelm them.
Sauron toppled Númenor, with no army, just guile. The Númenorians were the very best of Men, who, if you recall, easily conquered the lesser Men and set up their empire. They lived longer, were stronger, and had better tools, than your Englishmen.
Yet they also were subverted and defeated. After all, Sauron is thousands of years old, and is just as good politically as he is militarily. He could easily put on a fairer face and talk to the Welsh and the Scots, who might not be broken-hearted about the shattering of English power.
EDIT: "put on a fairer face" is being used metaphorically here, not literally.
What Sauron has to want are no alliances. Technically, the Welsh and Scots are vassals of the English king, which means a messenger will arrive at some point to demand troops. Any possible reason to delay sending these troops will be eagerly grasped at. Scotland will be ok, because Scotland is solid mountains and bog and waterlogged earth. Wales...
English power is based on heavy calvary in the medieval period. Wooded mountains are a great deterrent to this kind of power. Mountains full of holes, but not full of Dwarves are no deterrent whatsoever to an army of Orcs. Sauron needs an energy source, would coal do? Perhaps. The outlook seems bleak for Wales.
There's been mention of discipline problems with the Orcs. This might be the case on their own, but in battle they follow Sauron's orders, out of fear at the very least, and surely they fancy their chances against a bunch of Men, who are not being advised by creatures with two thousand years and more of tactical knowledge.
Food won't be a problem, they are not farmers, they'll eat their dead, and your dead too. It's not like Sauron cares about their welfare after all. The people who need the cropland are actually the defenders, who presumably won't resort to cannibalism right away, I feel they probably would prefer bread and rabbit over roasted orc and troll.
Guerrilla warfare is problematic for the defenders. In real life Harald Godwinson had this idea. He'd fought a war in the north, against Harald Hadrada. William of Normandy's army arrived late in the year, and was not provisioned for a winter campaign. Send the men to take in the harvest, burn whatever they could not carry, let the Normans winter in tents and push them into the sea in the springtime.
William's response was to start pillaging, burning villages, killing the villagers, who were kids, women and old men. Terror tactics, and they were quite effective at forcing Godwinson to battle.
Of course the orcs would do this, and then instead of burning or burying the dead, they would be cooked and eaten. Terrifying for the victims ( Old men and their grandsons, tortured and roasted) and brutal for their mothers, who will be watching all this while "entertaining" the humans in Sauron's army.
Ugh. Nope, your soldiers will want to stand and fight. But...
If you are not an Elf or from Númenor, or from Gondor, then a horde of Orcs is a great calamity. LOTR has the orcs getting slaughtered by the dozen, and so we mistakenly think that they are pushovers. They are not, and most of your army will be farmers with pointy sticks and shields, woodcutting axes, maybe double padded shirts or maybe some frying pans beaten into breastplates, or some boiled leather.
Technological advantage? Certainly not. Longbows won't be at the elven level. Armour won't be at the dwarven level. No palantir for them, to coordinate over distance, and no undead lich kings on dragons who can map out your troop movements. Crossbows won't work against a horde of Orcs, who will be attacking at night, because they can see in the dark, and who are as comfortable below ground as the Dwarves, and can sniff out humans easily, because of their excellent sense of smell.
Really, the thing to do, regardless of the roasted sons and ravaged wives, is to run away. Run to Wales, or north to Scotland, get your best negotiators and clergy on a boat and send them to the continent to organize a crusade, assuming your world has a religion strong enough to command the princes of Europe.
