To my knowledge there are no current claims about giant snakes or reptiles squirreled away in northern England, but the reason this film qualifies as a "cyrptid movie" is 1) there would had to have been a small colony of these snakes, since 1 was clearly killed--and yet, there is current snake resident of the cave system, 2) just because it's animal, wouldn't have kept it from being worshiped as a god of some sort...still it's just an animal. Granted, it does seem to have the power to turn people into "snakepires"--but, can't have everything!! The certainly acts like an animals when it eats it's most ardent worshiper without a second thought. Besides, there are a whole host actual enteries on the current cryptid list from England!!
Here’s A List Of Current English Cryptids
The above link leads to a site that is claiming the current Dartmoor beast is, like the beast of Bodmin Moor, a large black cat. The television series Fact Or Faked, investigated the claims and found something that did not look a lot like a cat, more like some mutant wild hog thing. Also, black hounds, reported to be ghosts, have been part of Dartmoor legend for hundreds of years. Conan Doyle's The Hound Of The Baskervilles is based on those stories. Point is, Dartmoor has a long history of people seeing unidentified black animals of some sort.
This is the only black dog currently listed on the Cryptids list on Wikipedia--which states that it is incomplete, from England; only it's in East Anglia, not Dartmoor.
This is not precisely English, it's actually Cornish, which is a Celtic land, but it's still part of England in a way, that say, Wales is not.