I would contest the ticket.
It's a year later.
You were directed by marshalls.
What signs were in place about parking charges? In order to send you a ticket, all charges and penalties have to be clearly displayed.
I found this information:
Private Parking Tickets
Private parking tickets are issued by non-public bodies for parking in areas such as supermarkets, hospitals and service stations.
These are not as easy to enforce as public parking fines, since they aren’t technically fines – the only way that parking companies can enforce them is by taking you to court. However, tickets issued by parking companies are often made to look suspiciously similar to public PCNs – and Parking Charge Notices, issued by private companies, even make liberal use of the same initials. Inspect your parking ticket carefully before deciding upon a course of action.
In terms of paying private parking charges, they work similarly to public fines – you are generally given 28 days to pay, and you will receive a discount if you pay within two weeks of the notice being issued.
If you receive a Parking Charge Notice, you should first find out whether the company that issued it is registered with the British Parking Association (BPA). You can do this by calling the British Parking Association on 01444 447 300 or by visiting their website.
If the company is a member of the BPA, they have the power to obtain your details from the DVLA in order to pursue you for the parking charge. However, if the company is not a BPA member, they have no such power.
If you think that the parking ticket is unfair, you should contact the company to challenge it, and their appeals process should be detailed on the ticket.
Alternatively, you may just be able to ignore it, since the company cannot make you pay the charge without taking you to a small claims court. As the cost of doing so is likely to be greater than the cost of your charge, there is a good chance that they will not take the matter further.
Without a court ruling, the company is unable to send bailiffs to your house, contrary to any threats they might make. They are also unable to clamp or tow your vehicle – in fact, doing so without legal authority is a serious offence, punishable by a fine of up to £5,000. If in doubt, seek legal help.