There is speculation that Jose Mourinho could be signed up by Manchester United, following the news of Alex Ferguson's retirement.
If so, it will put an end to rumours that the Real Madrid boss was planning to come back to Chelsea - where he was in charge between 2004 and 2007.
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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.