Not sure whether i've been unlucky to be caught or lucky not to have been caught all these years - those mobile units are the toughest to avoid - by the time you see them (if you see them, and they're not hiding in bushes), they've got you.
Don't admit to anything, let them prove their case or piss off.
Considering a detector but there are so many conflicting reports on good and bad ones based on not only the hardware, but the quality of the databases you update also.
That won't help for mobile units will it? Oh no, I'm gonna get started on the police now when I only just finished my rant on insurers!

I don't see their strategy as working to be honest. In Bedfordshire they've extended the limits on all the A and B roads waaaay outside the villages on those roads, and most often taken them from 50 or 40 down to 30. The effect (on me at least) is that on entering the limit forcing a cut in speed from 60 to 30 there is no reason apparent to the driver, the road appears the same as before... so people ignore it. Then when they actually enter the village there is no "change" as they already passed that point 2 miles back and so they don't slow down for the bit they previously would have had the limit changed only when it needed to.
They've also started putting up signs indicating cameras on virtually every road. There are no cameras, but one of these mobile units turns up once a year to 'justify' the sign. This is pure entrapment. If they wanted to improve safety they would clearly signpost the signs only at the specific dangerous corners... not the entire road. If the entire road is so dangerous that it is an accident black spot at every point on its length then it shouldn't be open!
Then there is the average speed cameras on the A14. They make things worse too. The problem is the slow container trucks sitting in both lanes at 50 and 51mph and causing a massive tailback 20miles long with cars nose to tail. The solution is to ban trucks from the outside lane. Forcing everyone to spend extra time watching their speedos and not noticing the brake lights coming on in front of them reduces people's reaction time by critical seconds. The crashes on this road have nothing to do with speed and everything to do with stopping distances, but speed cameras mean fines so...