I have gone via 'user options', 'my cookies' and pressed the 'expire cookies' button. The window goes blank then they all reappear and I'm still logged on!
I suppose I can trash all my cookies through 'Tools', 'internet options' but then I'll lose the cookies for other sites as well.
In the absence of any other ideas I'll leave things as they are. It isn't really a problem.
-------------------- Old Chemists never die, they just fail to react