Found this thread after reading again about the Atari find & wondering what became of similar buried Palitoy rumours, interesting to hear people following up on this seriously! Even found myself namechecked earlier on in the discussion
Digging up or drilling into old landfills was something I used to do quite often in my last job. Always quite interesting finding old crisp packets from long extinct brands and relatively intact newspapers. I did get a piece of Lego out of one in the Lake District a couple of years ago which I took home, but sadly no Star Wars.
Condition of anything surviving will just be down to how well the landfill was constructed and managed, how wet it was at the time of infilling etc. Rules have tightened over the years, one from the mid 80s might not be too bad. From experience some are bone dry with quite fragile paper pieces surviving, others are just a dark mush with occasional identifiable objects. A concern will be what else has been deposited there - anything like asbestos and it'll be a non-starter recovering things just on cost grounds. Also you always find people with strange tales about these places, so treat rumours with a degree of skepticism (one up in Cheshire next to a chemical works was alleged to have had barrels containing still-alive laboratory monkeys deposited there in the middle of the night, that kind of bollocks). Unfortunately the Environment Agency website which used to list basic details of operating periods of sites and permitted wastes is no longer operating, but you can see maps of the position of old sites with dates at groundsure.io - I've had a look at Lount where two large sites are shown (one municipal, one private) with a few smaller sites dotted around the area.
Happy to provide any advice on this, if you need someone to watch over a drilling rig or trial pits that could recognise obscure SW related bits of plastic in the sample tube I'm probably your man!
JF