Mayor Boris Johnson is facing a legal challenge by four London councils over his new plan for affordable rents - so why are they so opposed to it?
Boris' plan means that rents for new affordable housing can be set at up to 80% of the market price for an area.
However, Southwark, Islington, Tower Hamlets and Camden councils say that in their boroughs, 80% of the market rent is still unaffordable for most people. They want the figure to be much lower - Southwark council says it currently sets affordable housing rents at just 40% of the market rate.
Rents have increased in every area of the UK for the first time in 18 months and London saw the biggest annual increase.
The cost of renting in the capital has gone up 7.6% - meaning the average rent is now £1,110 a month.
Wales recorded the second highest spike; 5% rise taking rents to around £566.
Rents started edging back up again in March, after a period of falls caused by the seasonal winter slowdown. The further push up in April means average rents have returned to levels not seen since November last year and they are 3.9% higher typically than a year ago.
Rents have soared because of strong demand as would-be buyers have struggled to meet mortgage lenders' requirements and get onto the property ladder.
There have been some signs of the situation easing following Government schemes to help home buyers, which are filtering through to help people with smaller deposits. Lenders have reported seeing increased numbers of first-time buyers taking out loans amid better access to mortgages.
However, David Newnes, director of LSL Property Services who carried out the study, said that a lack of potential homes to choose from generally is helping to maintain the upward pressure on rents.
He said: "Landlords across the UK have increased the stock of rental properties by around 10% since 2008 - but the more fundamental squeeze is still coming from a lack of new building."
Mr Newnes said the rent increases will be particularly "keenly felt" in areas with a tough jobs market, as wage growth remains sluggish.
Mr Newnes said: "Landlords are lending a hand, and will need to keep taking up slack until the economy is on a more solid footing and improvements filter through to everyday wage levels."
The study is based on rents achieved on around 18,000 properties across the country.
The monthlycost of buying your own home is more than £130 a month cheaper thanrenting, research revealed today.
Rising rentpayments and lower property prices and mortgage rates now mean thatproperty buyers pay 18% - or £132 - a month less on average than those whorent, according to Halifax.
The lendersaid that average monthly costs for buyers of a typical three-bedroom house -including mortgage payments and household maintenance and repair costs - were £600 in June, against £732 in rent paid on the same type of property.
Four yearsago, the average cost of buying and owning a home cost 45% - or £324 - morethan the average monthly rent.
But,despitethe improvements in affordability, the number of new buyers in the market hasfallen by 33% in the last four years as lenders are demandingincreasingly high deposits.
The researchshows that owning a home was more affordable than renting in all 12 regionsacross the UK.
In London,the typical homebuyer pays 14%, or £177, a month less than the average renter.