Is it considerate or sexist to offer a heavily-pregnant woman a seat?

There were no doubt a few headaches among middle-aged MPs in the Commons tea room as they tried to fathom that one. The question arose after seven-months-pregnant East Dunbartonshire MP and Equalities Minister Jo Swinson came to Prime Minister's Questions only to have to stand at the back because no-one offered her a seat.

It is not clear whether Duncan Hames, the Liberal Democrat MP for Chippenham, was present - he happens to be Ms Swinson's husband.

A source close to Ms Swinson thought the ensuring furore was quite absurd, suggesting that the idea she could not stand on her own two feet just because she was pregnant was "quite sexist".

David Cameron, however, apparently took a different view. His spokesman insisted the Prime Minister would give up his seat to a pregnant woman on a bus, though given that that would require the Prime Minister to travel by bus, it may not be put to the test any time soon.

What will MPs do if it happens again next week? The Lib Dems had better save her a seat.