I parked in a bay in a council owned off road car park the other day
I came back to find a ticket affixed to the car.
Upon reading it it states i was not parked in a marked bay.
I was parked in a marked bay, but on leaving i saw it had reserved painted on the ground.

The ticket has been issued by huntingdon county council
I had a valid pay and display ticket
There was no signage except for the road paint in the bay to suggest it was reserved

I've subsequently found out the 2 parking bays (in a car park of 15 spaces) are for the cars of the parking wardens!

Can anyone suggest what to do?

I'd suggest the PCN is invalid as it does not accurately describe the contravention, per Metrick v Camden and Burnett v Buckinghamshire.

The PCN should accurately describe the contravention in line with the Traffic Regulation Order that creates the prhibition or restriction. In this case, something like "parking in a reserved space when not authorised". Putting down "not parked in a marked bay" is just wrong, factually and legally. It may be that the bays are not even reserved in the TRO and hence the PA made the contravention fit the facts!

Scan in and post the PCN (front and back) as well as there may be more errors on it.

Also, what is the date of issue on the ticket? Does it say Road Traffic Act 1991 or Traffic Management Act 2004?

Hi sorry for the extended delay in replying, i'll scan the ticket in tomorrow when i get home