building on someone else's land

[db music co]

our flat is a 4 in a block type and we have the upper flat, our council built a disabled ramp for the grnd floor flat and used 6m2 of our land and 12m2 of a shared path. This was 12 years ago when my mother in law who was 93 lived there and it was an ex council house which I think the council still though was theirs and therefore never asked permission. My brother in law was left the house and sold it to us in2006. however the plans were not changed and there is no disabled is living there now. Is there a time limit on this or can i make them remove it. Was it illegal for them to do this in the first place