If he goes from Detroit, your only choice is Delta. There isn't any First class, only Business Elite. The upside is that LHR is a focus market for Delta and he'll be on a 767D with lie flat beds in BE. I was very pleased with my experience earlier this year. Unfortunately there is only one flight a day from DTW and Delta's website will try really hard to route you through Atlanta. If you decide to go with Delta, you want flight #6 outbound and #5 on the return.