After 300 years, you may find some surprises without human intervention.
Big(ger) Cats. There's a big push to reintroduce the Eurasian Lynx in England. While it isn't legal to keep them, it is quite possible that there are a group of people with a secret population. There's also been mysterious, albeit unsubstantiated, sightings of large black cats in recent years. Add to that your ordinary, everyday, house cat & special breeds. A Maine Coon can be about 18 pounds. It would take just one of extraordinary size, that's enthusiastic about breeding, to up the size of a house cat. With all the deer around, and mid-size prey, it would make sense for them to get a little bigger and take advantage of all that food. As quickly as they breed, I would not be at all surprised to see a 20-50 pound cat derived from formerly domesticated cats in 300 years.
Thick Woodland Aside from the moors, vegetation and trees will take over, even in highly urbanized areas.
Adapt or die Most sheep, which are bred not to shed and rely on shearing will die or be unable to breed because of their coats. Cows are not built for the woodland, so most of those will stick to open field areas, as will most horses. Most cows will die. Pigs are highly adaptable and grow wild fairly quickly, so there would be a good population of those. In fact, I would say one of the most dangerous things to any human who happens to wander about in this new/old land is going to be pigs. They weigh several hundred pounds. Regular feral pigs, as linked there, are not too agressive, but the longer they spend out, generationally, the more territorial and likely to attack that they get. Pigs, also, are omnivores and will eat anything. After 300 years, these will be the most dangerous things in the woodlands. Chickens, might survive, but would have to be less conspicuous in plumage, to survive things like hawks.
Herds You're going to see herds of horses and deer on the moors and sometimes the woodlands. They will move with the seasons.
Foxes There will be an abundance of these. They will likely fight and kill formerly domesticated cats, of which there will be plenty because of the large starting population. They will also feast on little animals and are great opportunists when it comes to caresses. They will compete with hawks and stoats.
Wild dogs I believe wild dogs will start to revert to wolf-like behavior, and they will work in packs. Besides the wild pigs, they will be very, very dangerous. Wolves weigh from 40-175 pounds, a pretty wide range. But their strength is in packing up. A pack would be able to take down the weakest of the large herbivores and will likely be the apex predator for the island.
Addendum to Pigs: If you stick to the human trails, pigs aren't aggressive--but if you wander about the woods, it's going to be slow going. Most humans won't fight through the undergrowth, so there's going to be things called "pig trails." These are basically pathways that have been created by the egress of pigs. If humans are going to be coming back and experiencing this land, it's pretty likely that they will take the easiest route in the over grown woodland. That's going to be a pig trail, which means that they will likely be running into pigs. There will be general wildlife trails throughout the woods (kind of like a public road) but there will also be "private roads" left by pigs. We humans can't see the no trespassing warnings left by scent, so...