Either no one else has had this problem, or no one else has been able to fix it.
Here is an update of the situation. I removed the lock from the under seat housing. this was quite a fiddly job, but eventually you can get the lock and metal bracket out of the housing. You need to be able to unhook the cable from the lock. once done, you can pull on cable that connects to the under seat lock.
In my case however, it appears that the cable has come loose on the other end !! So I can tug on the cable and it should be dis-engaging the lock on the other end, but it ent.
looks like I may have to take the bike apart to get to that.