The only reason you are there is because they have a runway and a hangar you can use - both of which cost them £££ and the costs have to be recovered from the people who are using them. Had it been a farmers field you would have trailered it out and got it home PDQ. Because your aircraft is in a hangar next to a runway you have made a decision that it is more convenient for you to leave it there rather than take it home - but why should the airfield pay for your convenience?
It's not nice when you end up in a situation like that and the costs start to hurt, but airfields are businesses and if you are using it you should expect to pay.