I recently parked in a railway station car park operated by NCP. On my return I found a Parking Contravention Charge Notice had been issued because I had not parked between the bay space markings. This was true because on my arrival I parked in a line of cars which had one space vacant. I was not aware at the time that NCP regard this as an offence.

There were plenty of other spaces available but I chose to park 'tidily' and use the single space which presented itself. NPC can not claim that my parking deprived them of income given the number of other spaces which were available.
I see this as a minor transgression of NCPs regulations yet they are now demanding a £50 charge from me in the next 14 days 'or else'.

Am I obliged to pay this charge or should I contest it as being unreasonable for the 'offence' committed?