Every Single fishing pot marker/whatever in western med I have come across has shown up on radar. Spain france, corsica all the same. They all have radar reflectors. The fishing boats have a stack of them which you can see in harbour- all the raflectors. I think that would pretty much sort it in uk.

Admittedly tho, there aren't as many, prhaps cos they are forced to have radar refelectors - and not little hiding-behind- the-waves ones either - these float with submerged counterweight somehow so they are 2metres high in the water. I felt safer coming into antibes at planing speeds in the dark than I would do in daylight in west country