Mayor Boris Johnson will be in Croydon North today ahead of next weeks by-election in the seat.
He will campaign alongside Conservative Party candidate Andy Stranack.
On Thursday Ed Miliband will join Labour's campaign.
More top news
The plaque at number 16 Cowley Street in Westminster marks the brown brick Georgian townhouse where Sir John lived for 31 years.
A man reportedly armed with several knives has been arrested in Whitehall on suspicion of planning a terror attack, police have said.
Metropolitan Police officer, Tom Harrison, has been crawling the course since the race began on Sunday morning.