Most airports in the UK provide you with an alternative to long stay parking, which can be quite expensive. They provide what's called 'Short Stay' parking. Short Stay means you can park up, get a ticket and check the arrivals. Once you're ready to leave, the normal procedure would be to get your car and pay on your way out, which in most cases will be as cheap as chips. In most cases this is what happens, if not, feel free to leave your own answer below. Remember, don't pay more than you need to, and get the cheapest airport parking out there.

 This website is for all airport parking. This is a great site.
Http://www.holidayextras.co.uk/