Building regs

[hermana]

We are in the process of selling our house which we bought in 1965. It was built in 1897 and was a wreck when we bought it. - riddled with dry rot and woodworm. It was treated and we replaced floors, ceilings, joists etc. We subsequently installed central heating, rewired, removed walls, replaced windows and built a porch on the back door. The majority of this work was carried out in the 1960s and 70s. We added the porch in about 1990 and shortly after that we installed a roof window in an existing attic room and moved some walls to create a large bedroom and en-suite toilet and shower room from two small bedrooms and a corridor. No structural work has been carried out for about 12 years but we are now being asked for building regulation approval which we don't have. If we ask for retrospective approval could we be required to undo any of the work and what is likely to be covered.

Help please
Hermana