In the UK a very quick Mayday call and a thirty seconds or so of 7700 on the transponder will get you no end of help, D&D will tell all the local airfields about the problem and then if your primary trace on the radar heads their way and you try and land you will get a green light from the tower along with all the fire trucks you will ever need if you head for a military airfield, all without you having to talk to them on the radio that you have turned off.
Exactly. I may add that in the UK you'll never land far from someone (some remote parts of Scotland excepted), but if you fly in places without human presence, letting ATC know what's up is, IHMO a very good idea. You don't even have to travel very far for that, parts of central France or Spain are pretty empty.
If possible, I would therefore do a quick Mayday, hit the squawk ident button and then shut everything off PDQ.