Demand in the rental sector has rocketed as people have been unable to buy their own home, either because they cannot raise the deposit needed or meet lenders' toughened borrowing criteria in the difficult economy, which has pushed up the cost of renting.
The Royal Institution of Chartered Surveyors has warned that it is currently possible for people to set up a lettings agency without appropriate qualifications, knowledge or understanding of the rental process and it is not compulsory for them to conform to codes of conduct.
Several calls have been made for better protections for people living in the private rental sector in recent months, with Shelter reporting in September that almost a quarter of people feel they have been "ripped off" at some point by letting agents' charges.
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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.