Zac Goldsmith MP joined the Mayor and hundreds of others in Barnes at a rally against Heathrow's third runway.
Richmond Council, which serves residents who live under the airport's flight path, is currently leading a referendum on the future of Heathrow.
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Calum McSwiggan posted a photo on Instagram as he lay in a hospital bed after the alleged attack.
The London mayor publicly backed defeated candidate Owen Smith in the contest which saw Mr Corbyn re-elected party leader.
Police described it as a "growing sink hole" and it's unclear when the road will reopen.