The following link is worth reading and the glove box advice leaflet is worth printing and keeping.
NOTE this refers to PRIVATE car parks only ie supermarkets etc.
For council operated parking administered by wardens and the police there is a link advising what to do.
I was ticketed in a private car park that belonged to a closed down bowling alley, there must have been someone waiting to slap the ticket on as it was done within 2 minutes. The advice at the time was to ignore everything including solicitors letters which I duly got and ignored. The advice was good and that was the last I heard of the matter.
However since 2012 there has been a change in the law and whereas before the company chasing your "fine" had to prove that you were driving the vehicle now its the owner that's liable. A typical tory leg up to their mates who own these private parking companies in my view.
The difference is that whereas parking on double yellows is an offence against the law, private schemes are based on the signage on display at the car park. The signs should be visible and by reading them you are deemed to have entered into a contract and anything you do outside the conditions are deemed a breach of contract and the company are entitled to retrieve damages.
Note damages are supposed to be a fair estimate of the costs incurred by the company due to your breach. Which on a half empty supermarket car park is in effect a big fat nothing and nowhere near the £60 quid that they threaten you with.
Other key things to note:
Debt collectors have no power to enter your property or make threats to you or take anything you own.
If in doubt call the police.
Bailiffs on the other hand are sent by the court and you will have had correspondence from the court by the time they arrive. They do have powers to take your property.
i have also had personal experience of incorrectly displaying a blue badge.
The first was not setting the clock correctly and the latest is not displaying the badge.
I wrote to the relevant local authorities and have had fines rescinded so definitely worth a try.
The clock is a bit of a legal grey area anyway; not displaying the badge I explained I forgot and was on my way back having remembered but due to pd was too slow to stop the ticket.
Note Clamping on private land is illegal. Only the police, local authorities reps and DVLA are allowed if in doubt call the police. However, a closed exit barrier is legal.
The continued letting of private companies overseeing public car parks has led to increased costs and the disabled subsidy disappearing. If you havent got a blue badge I would recommend getting one.