Chain jumps off large chainring under high torque

[cameronpack]

Well, managed a 22mile ride around the beautiful countryside up here today and not a cross word between me and my bike. I think you are all correct that the 122.5mm bottom bracket I have now used may be a smidge too big, but I managed to adjust everything fine and had a smooth ride today.
Thank you everyone for all your help.
Cheers
Cameron