help re shop car park fine!

[stinkyo]

Hello, I'm new on here so I may be on the wrong bit for my question? But I hope you can help anyway.. I work for Tesco on a retail park. Behind the shops there is a staff area for parking, about 10 bays behind Tesco and a bigger area behind the rest of the shops. After about 4-6 months of working for Tescos I had a staff permit which would allow me to park behind or in front of shop (as long as I was well away from the shop) and the permit was on display. I was told I could not park in front of the other retail shops. I have been in Tesco for a year and a half now and about 6 months ago started parking at the back of the shop as my car had been damaged numerous times in the front with trolleys. Last night I finished work at 4pm (although wasnt meant to finish till 10pm), and went round to my car at the back of the store. there is a laybay behind Tescos and also a carpark to the side and behind the other retail shops. I park in there as usually all the spaces behind tescos are normally gone (only about 10 there). When I came out my car had been clamped and there was a notice on the car that I had to pay a fine of £50.00 for release. I was in tears as I felt I had done nothing wrong, this was our car park! Went back in and was told oh no we were not allowed to park in this car park - only the other shop staff!! I dod not know this. A duty manager came out wth me and contacted the company, got them to come out and remove the clamp but they said I still had to pay the £50!! Went up today as am positive there is nothin to say no Tesco staff in this car park and there isn't.In fact as you drive up to the car park behind shops it says tesco euro car parks - i took a picture of this - and I checked again today and the signs in the car park say staff car park and service area only-display a valid permit or be fined £50..nothing about clamping or Tesco staff. I had a valid permit and wasnt aware it was invalid for that area?! where do i stand? Please can anyone advise me? (ps i know this thread is on another , but have only just realised how how start new thread!!)