How Far Is Wokingham From London?

How do you define London?  Not being funny, but a city of 4-8 million (how many depends how you define the boundaries) covers a lot of land.

To the edge of London (inside of M25) only 14 miles or so (20 to drive it),
To central London, 30 miles (40 miles to drive it).

I found a source that reckons you can drive it in under an hour, but I'd be so impressed if anybody managed to drive it in under 90 minutes.