The IMF is a members' club. The UK and France pay in, and can therefore draw out if they need.
We last needed an IMF loan in the 70s.
The IMF developed out of ideas from British economist John Maynard Keynes, who saw the terrible damage done to the global economy in the 20s and 30s of the last century due to lack of an international monetary body.
It is politically embarrassing to have to ask them to loan you though!