I love this phrasing! Is this a common figure of speech in Britain? Is it lighthearted or pretty vulgar?
Oh, and as to the OP:
30 Signs Your SO May Be Cheating
Signs of Infidelity II: Revenge of The Other Bloke’s Hampton
Sometimes this is true, though. My first husband bought me roses for no reason one time. I said to my co-worker, “I wonder what he did wrong that I don’t know about.” She said, “Oh, that’s mean!” I was right, though. We’ve been divorced three years and I’m still finding out stuff he’s done to me (like not filing our 1999 taxes and somehow stealing the money order made out to the IRS for my half of the taxes.) I’m thankful every day that we never had kids together so that I never have to talk to him again, ever.
Yes, but a girl might also do this because she suspects her boyfriend/husband of cheating or flirting. She may be trying to make him feel bad about something he may have done by being really, really nice to him.
I know this from personal experience as well. And ya know what?
It worked! 
I have heard a wife’s unexplained yeast infection (out of the blue) may be caused by the husband double dipping, since the body chemistries are different, and the male can be an asymptomatic carrier. Obviously not all cases are from this cause. Probably.
The problem with this logic is the fact that women can get yeast infections from an almost endless list of causes: wet bathing suits, tight jeans, silk undies, certain foods, taking baths…on and on. I doubt this would be a good way to “catch” a husband cheating given all the ways that a woman can develop this infection.
Lightheated AND vulgar. Also common usage.
Hampton = Hampton Wick = Dick.
btw Hampton Wick is a place. So is Littlehampton.