I've read a couple of topics similar to my question but couldn't find a direct answer to my query. When creating a new timber stud partition to then fit a fire door lining/door etc, do you have to leave a gap between the rear of the frame and the new stud work? I created a new stud partition and fixed the lining tight to the stud leaving no gap (using appropriate length fixings, positions etc) and I've just been pulled up on this saying there HAS to be a gap which you then fill with an appropriate mastic/foam. Surely if there is no gap at all then this is better then making a gap just to fill with mastic? Appreciate any advice. 

You need to look at BS 8214 Table 2 to 5, all suggest some form of gap that should be filled.