This isn't the sort of thing that can be kept under wraps. Is there any way that accessible records can prove he's telling porkies?
This sort of incident is handled by the Fighter Controllers and an FOI to Boulmer for records of all suspect aircraft that have entered UK airspace might well turn up some info.
The situation does happen and people very senior at whitehall do get phone calls to release aircraft for scrambles against none identified aircraft. Have a look at the boulmer web page