Do London's Conservatives support cycling? - He said that the City of London is currently considering introducing a 20mph limit within its borders ... but the Conservatives were "not in favour of introducing a 20mph limit across London". Don't know what definition of London is being used here, but in central London I can't see it making much difference. Borisbiking across London I've rarely been outpaced by traffic, so maximum speeds must be around 15mph. That said, Blackfriars Bridge, while I don't use it hugely often, is fast and sometimes rather hairy.