Thanks to all & thanks for the welcome.

I realised after posting this question that of course, they cannot MAKE you use the reurn portion. I mean, for all they know, I might be run over by a bus on my way to the airport. Or indeed be dead.

I've read THIS:

"As for buying a different return ticket for your trip to Europe, you could buy a completely new return ticket to Europe and just not use the one on BA. Or you could just buy a one way from Europe back to wherever you want to go."

... five times and must confess, I do not understand what you are telling me ClimbGuy.