How many petrol stations are there within the M25 in London?

Question

I was asked to solve this in a job interview and they didn't know the answer either.

Answer 1

There are no crop circles in Hyde Park thus far this year, but of course they, what dunnit, could strike any time soon.

Petrol stations?

There are two near where I live.  A third is being converted into one of them supermarket local thingies, but I don't think it will sell petrol which is a pity becuse the supermarket who now own the sight and got if from the ESSO company, keep handing out X-off petrol at our pumps when you spend £5,000 or less.  Or some such waffle.

Answer 2

Yell says 413 in Greater London. The area within M25 is somewhat bigger.