Pete,
your right about the brakes beeing stuck even without using the handbrake..
It's likely to be because we all reverse the trailer into the parking area, and there fore the braking is on, when we leave the trailer.
( I really can't figure out how it works on my new trailer

, there is no brakes when the trailer is reversing. But if I slam on the braks all 4 wheels on the trailer come to a complete stand still, so they must be working. Tried this in Copenhagen city, when a moron drove out just in front of me, if it hadn't been for my rib, his car might not have been so pretty afterwards...
I drive a large 4x4

)
There is one workaround on this.... When you have the boat in the right spot, drive a little - very little - but fast forward, this way the brakes releases, and the boat is still in the right spot.. (And don't slam on the brakes afterwards, try it a few times, where there is plenty of space)
Don't try to do this by hand, I don't think it will be enough to release the brakes completly. Unless you are on big ..... (something)
Regards
Rene