This article nailed it for me:
HERE are some things I know by now:
Men love to play up their sexual achievements in the US.
Men usually play down their achievements in the UK.
I admire the low expectations of British women.
In America, I see bumper stickers on the backs of cars belonging to proud parents, proclaiming how smart their child is. Crap like, “Grade A Student” or “Member of the Honor Roll”. I never see these in the UK. But I wonder what they’d be like if they existed.
Given the British nature for downplay, I think they would read: “I Have the Fattest Child in Town” and “My Daughter’s a Slag’.
from here. Very very funny..