Quick update:
I have received a replacement Surface Book today. There doesn't seem to be any information available about what the problem was and, in fact, I only know it's a replacement because of the serial numbers - the info on my Microsoft account is fairly ambiguous. (FYI the tech assistant had noted my issue as 'overheating')
Anyway - I'll let you know how it's running once I get all my software reinstalled and try out a couple of the problem programs.
Cheers,
Dan