Timo, it's probably easier for you to buy a car from wherever Steve recommends - at least that way the previous keeper on the logbook should have a bit of 'prestige' in their postcode - because that is what matters, right? You don't want the person who buys a car from you looking at the logbook and thinking "Oh dear, this chap has been to Milton Keynes" and walking away from the deal.
Having said that, I tend to avoid buying any car that has spent its life inside the M25, but that is mainly because they're often battle scarred and have spent hours upon hours crawling in stop-start traffic, and partly because I can't be arsed going to London.