There is a small lesson here - that seems to have been missed. If departing from your planned route (and we all do this constantly), TALK TO SOMEBODY. This is the sort of thing ATC are paid for!
A couple of years ago I was routing somewhere not a million miles from Southend, and decided to modify my route slightly through the overhead of an airfield - at a nice safe 3,000 ft.
Not wishing to cause offence, I called them up on RT about 15 miles out, explained my intentions and asked if there was anything to affect me. Rather coldly, they pointed out that actually they were in the middle of an airshow, and would very much appreciate it if I went elsewhere - so I did. No drama, no prosecution (another statistic possibly about the lousy NOTAM system at that time, which I HAD checked quite carefullly, but failed somehow to note this). I'm sure that the fellers in the tower at Clacton said some fairly unpleasant things about me - but far less unpleasant than had I just carried on into what I thought was open FIR and possibly preceded our Belgian friend in his misdemeanour.
G