Every event I have been to in the UK, we are asked to Sign that we have insurance, BUT it is never checked....

Why, well the reasons I have been told is that if someone checks that you have insurance, then it is THEIR call to say if it is

a, Valid
b, appropiate
c, Up-to-date
d, real

If you do not ask for proof, the responsibility for the provision and validity lies with the person signing that they HAVE insurance.

I have been to ONE EU regatta (30 years ago) that required us to present our insurance documents, but none since.