Hi and welcome Dave.
Depends on description of land on your 'deeds if they still call them that, have you used a solicitor for the purchase?
We had a similar situation nearby, but much smaller, only 7 lots on a rubbish field near the river.
Vendors wouldn't sell if you checked with local planning first.
No building supposed to be allowed, various people have tried and council put enforcement notices on them. but it appears someone has done a lot of work on one, lots of trees hiding a caravan.