Ways to support #7: Help me plot a route round London!

On Friday 1st May I'll be running a marathon on the streets of London. This is great, except that my geographical knowledge of London is limited to the Northern Line between London Bridge and Kings Cross.

Can anyone help me with a route? I don't mind laps or there and back again courses or even the odd hill, but I do not want too many crowded pavements, busy roads or anything that means stop-starting.

I was thinking of parks - Hyde, St James... Green? running round one and then running to the next one and so on. Any ideas anyone?