squatters rights or not. we live in a

squatters rights or not. we live in a semi detatched house. There was an older man who owned owns the other half. He used to come out once or twice a yeara and basically destroy his part the fgarden, however, he never used the downstairs there being an entrance to the upstairs which was self contained/ He used it  to sleep for a week or two whilst here and to stack hundreds of papers and empty bottles etc.  Then he got involved with a woman and apparently married, she objected to him coming here to do what appeared to be a job he hated and did because he had to though why I know not. So he stopped coming and abandoned the place. MY husband has had to do repairs on it since then the roof or anything that arose ( externally) ithas been about four years  since he visited this house though he has been to the village and stayed there a few holidays. It is being left to decay away. The windows are broken and its all overgrown generally neglected.We pushed in the shutters of the part where the windows were broken and saw inside, and its a huge mess of rubbish and ruined old furniture mould and woodworm, piles of papers bottles and anything rubbihs stacks high. otherwise filthy and the wall that adjoins ours is mouldy from damp from the terazza.  Now we have not been into any other part of the house, but the damp from it is coming through the walls of our two upstairs bedrooms causinfg black mould.IN our opinion he has left it to rot and we want it.We dare not contact him ( he is a difficult person anyway) becausse he will  wake up and become nasty even though we have done maintenance work. We want to know if we can use it, it we get rid of the rubbish put a coat of paint on the rooms and use them not for sleeping or anythng just as storage. I had wanted to rent it off him but I am sur eknowing him ( he is wealthy) he wouldnt  do that having nothing to gain. What I want to know is if we clear out the room we have seen and give it a acoat of paint and clear up the damp mend the windows etc could I put my dozens of paintings in there and use it as a studio without him coming or something coming and ddestroying my things? what can we and cant we do about the place?