definitely call Dept. Fair trading, and they will direct you to the proper area if that isnt it... definitely not right! like others have said, he can definitely take his car back! He definitely should have been notified before any more work was done that wasnt on the quote! and im also interested as to what could possibly cost an extra $4k!!! should get a brand new engine for that!! :O
I daresay that if they're trying to rip him off by charging an extra $4000 ONTOP of the original quote, that the original quote was probably a rip off too :/