Look through some property websites and you can see the advertisements: the phrase you are looking for is contre services - when a room in an apartment is offered, sometimes "free", in exchange for services.

Sex for rent is the extreme end of an extreme problem which is catching swathes of France's most vulnerable people - the young and the poor - in its grip.

France, the government admits, is in the grip of its worst housing crisis since the end of World War II.

Of course, sky-high property prices are hardly exclusive to France.

But some combination of circumstances has left the French - and especially the Parisian - rental market horribly stretched between supply and demand.