Possession of Property since more than 30 years

Sir, My father had taken a property on Rent from someone , residing in UK some 30 years back. Rent deed was made that only and there was also mentioned that we can only use it for LPG. Deed was made from someone who had power of attorney(WHO was brother of the owner's son-in-law). The owner died and the person who had power of attorney also died few years back. We have also transferred the gas agency to someone else after my dads death. NO one has come since 2007 to collect the rent. Now, we aren't giving any rent but only deposit property tax only. Electricity Meter name is on my mothers name. I , now want to open a garment shop but I am afraid the son-in-law would complaint in police or something....cause it only says abt LPG allied items and he says the poperty belongs to his father in law (alhough he has no legal right). He had once complaint once when we tranferred the gas agency but at that time we had 51% share so he couldnt prove. He has got some connection in police so he might harrase us. Is there any legal right I can have ? I am not sure is the rent deed is still valid ? I dont remember....if the rent deed was made of any number of years ?....I think it had got expired though.....will see again. Can i pay previous rent of 3 years and do want I want in terms of business. somebody also told me to take stay order from court in advance. Pls help