London Mayor Boris Johnson has been wheeled out throughout the year in promotion of the RideLondon cycling festival.
The regular rider will take part in the 100-mile challenge on Sunday.
"My team has told me I will never make it," Mr Johnson said. "They think I am too clapped out to cycle 100 miles but the more they discourage me, the more determined I am to have a crack."
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Clocks will go forward 30 minutes so there is half an hour more daylight in the evening when energy consumption peaks.