Building Regulations problem

[Barry]

Hi. I bought my house about 7 years ago. We have an integral garage, and the rear half of the garage had been converted by the previous owners years ago into an office/playroom with a seperate toilet. I am now in the process of extending the front of my house which includes slightly extending the front of the existing garage. I have had planning permission approved, but I've received a letter from the council to say that original conversion was without the appropriate permissions and without a building regulations submission. I have also been told that the new works effect the old converted area and we have to rectify the unauthorised works prior to completion of the new extension. But the new extension does not in any way effect the original works - can anyone advise on where I stand and what my options are ?