Standing outside churches would be a waste of time, weddings are exempt from licensing.
Yes you would think it quite easy to find unlicensed vehicles of any sort simply by going to places that they are known to frequent such as school proms, Royal Ascot, and other high profile sporting events such as cup finals. The reality again is that traffic is already chaotic at these events and setting up check points just makes things worse so I guess they don't bother. I have personally pointed out to police officers at Royal Ascot, vehicles that were not even registered only to be told that nothing can be done because it is private land.

Again nothing will be done when the vehicle leaves the course because of the already chaotic situation.
Next time you are out and about just take a look at vehicle registration plates, how many are now eastern european? These people don't have road tax, mot and probably no insurance. They don't get done by speed cameras because the DVLA has no record of the vehicle, they don't pay the congestion charge for the same reason. I have seen stretched limousines still showing American plates so what chance is there unless when stopped they are taken straight off the road.