[edgley]

Okay, not that I asked you to try my settings, but it would have probably been quicker too than to logon here and post that you are not going to :)
(actually I am not even sure what settings I have asked to be tested, I think I have my trackpad set to the same as you)

Support has come back with the reason for my problem.
It seems that I am doing the double click at a different spend on each machine.

I have turned up the speed on the MBP and now double tap slightly slower and it works every time; phewie!!