I'm not convinced suggesting not taking the job is a wise move. I get your opinion Unknown but I'm equally a contractor and the court acknowledged that and the vulnerabilities that come with it.
Devils advocate being played here, Oneofmany doesn't take the contract then doesn't find any work for a period of time, what are you suggesting would then be considered? Assuming Oneofmany has been in employment continuously for several years if not decades, that will also be frown upon. No court in the land is going to base a settlement on an income of £0. They're going to take into consideration his skills, past earnings, etc so are at least going to arrive back at £65k.
From my perspective, Oneofmany taking a contract for 3 months on higher pay doesn't automatically result in him now being considered a higher earner with higher earning potential. He's taken temporary work, which carries less benefits and greater risks which compensate him with higher pay over a period of time. Should he choose, he can simply increase his pension contribution so he's paid the equivalent of £65,000 a year and benefit from the extra pension savings. No court is equally not going to hold this against him.
Finally, assuming you've worked in your section for a period of time, you're well paid with skills, should you choose not to take this job and be out of work, how easy is it going to be at some point to find work again. The longer you're out the game, the more likely you're going to find it more difficult to get back in.
I appreciate Unknowns thoughts but personally I'd be snapping the recruiters hand-off for work.