Not huge, as you see from the report BA is not witholding payments at the moment.

Given the size of its fleet BA wins from this. At any time there are full aircraft crews sitting in hotels at Heathrow, in full uniform, ready to go at a few minutes notice in case of delays to incoming aircraft. Imagine that for a job - you spend a full shift, every day, in a hotel in full uniform waiting to go - and you rarely do.

Smaller airlines can't afford to keep fully crewed aircraft sitting around 'just in case'.