I received a ticket from APCOA for illegal parking - the only thing is, I didn't know I couldn't park there. The ticket was some time ago, and since then, I have received a letter from their debt collectors (Roxburghe). I didn’t enter into a contract with them, as I wasn’t aware I needed a ticket to park where I left my car.

The previous time I had gone there, there was no charge for parking, but unbeknown to me, the situation had changed in the meantime. I vaguely recall a couple of parking attendants, who saw me park up and waited for me to walk away before issuing me with a ticket.

Do I have to pay them? Are they legally allowed to enforce this?