Well, you overstayed which is a breach of the terms and conditions of parking on that land. Were you aware of those terms and conditions? If not why not?
If you think you are bang to rights and do not want to fight it, then you can take advantage of the mugs discount. If not, you can fight it but there are no guarantees that you will win. It would all depend on which bulk litigator they decide to use. For most of them, you can often win on technicalities. However, the decision must be yours.
If you fight it, then we will advise on each step of the process, which is likely to go all the way to litigation. The odds of it ever getting as far as a hearing in court are very slim, but not impossible. If you were unsuccessful, you would likely be looking at about £200-£250. If successful, £0.
Even after a claim is issued, you will still be able to go through mediation and try and reach a settlement for less. This could be decided once you which bulk litigator they are using.
Decisions, decisions.