We had something similar. We spoke to the local building inspector who requested that we exposed the footings for his inspection which we did. We ended up knocking down the existing extn and pulling out the footings! At the end of the day, the BI needs to be happy so you may as well engage them sooner rather than later.
Depending on when it was done it might have structural Calcs and drawings logged as part of its building regs application with the council. You can find these if they exist by a search on the councils website, planning/building regs section. Each councils website is slightly different so can't give you exact instructions sorry. A chat with the building regs officer or a structural engineer would then help.