This rental car agency is far, far superior to any of the majors located at London Heathrow or Gatwick. Note you need to reserve a month in advance as they sell out. They're far more reasonable (it was a third of the price of the others such as Hertz or Europcar) and the company is fair and honest.
After you provide all your details (a copy of your drivers license etc) they confirm the rental and you let them know which office you want to go to (I chose Guildford, their main office, but should've asked for Chertsey, which is right off the M25). Someone will meet you at arrivals with a sign listing your name. They'll drive you (in the car you're renting) to the office and you finalize the paperwork. (Note, if you have too much luggage to fit the extra driver in the car, let them know and they'll meet you with a larger van).
I suggest you also ask about "full cover", which means they provide full insurance on the vehicle. It's a minimal cost and well worth the headache if you have an accident. I used another agency in years past which they bought out (Car Quest) and the full cover paid the cost of a wheel I managed to explode on a "traffic calmer". Calm my backside, I was NOT calm when that happened.
To return the car, you take it back to their office at the agreed upon time and they drive you back to the airport. Very easy, well priced. FYI, the drivers are independent contractors and appreciate tips. :) read more