Conversation so far:
When did Tom Simpson move to Brittany?
Tom Simpson moved to Brittany in April of 1959.
Why did Tom Simpson move to Brittany?
Tom Simpson's National Service papers were delivered. Although willing to serve before his move to France, he feared the call-up would put his potential career at risk.
What did Tom Simpson do once he moved to Brittany?
Tom Simpson applied to local cycling clubs, and joined Club Olympique Briochin, racing with an independent (semi-professional) licence from the British Cycling Federation.
How long did Tom Simpson race in the Club Olympique?
Did Tom Simpson accept to race in the the eight-day stage race Route de France by the Saint-Raphaël VC 12e, and if so, did he win?
Tom Simpson won the final stage of the race Route de France by the Saint-Raphaël VC 12e, breaking away from the peloton and holding on for victory.
What did Tom Simpson do after winning the eight-day stage race Route de France by the Saint-Raphaël VC 12e?
After this win, Tom Simpson declined an offer to ride in the Tour de France for the professional team.
Why did Tom Simpson decline the offer to ride in the Tour de France for the professional team?
Tom Simpson had contract offers from two professional teams, Mercier–BP–Hutchinson and Saint-Raphaël–R. Geminiani–Dunlop, which had a British cyclist, Brian Robinson.

Question: What professional team did he decide to sign a contract with?
Self-contained rewrite: What professional team did Tom Simpson decide to sign a contract with, Mercier-BP-Hutchinson or Saint-Raphael-R. Geminiani-Dunlop?