tmmorris' post above reminds me of something I was told by my first boss in a flight test department, which remains excellent advice.
Before making any aeronautical decision, always run through your head the phrase "at the subsequent board of inquiry"
That said, if he had the kit and training, he absolutely could have climbed into IMC and asked for a diverting IAP into Southampton. He might be embarrassed with paperwork to do - and would be wise to declare a pan. But if he and the aeroplane could do it, it's a legitimate set of actions, albeit emergency ones.
G