As a complete outsider and knowing nothing of the circumstances of this club I would still like to suggest that twelve hundred squiddleys for a month's parking (however irregular) is excessive. At my local airfield you can park for a month under the cover of your own brand new hangar for £180. I would say the local council have made fools of themselves by raising this invoice - it's a joke.
I appreciate the aim is for the charges to be punitive in this instance, but it looks to the casual observer like all sense of reason and balance has been lost in favour of emotion and loss of personal control.