Rents have fallen year on year in London for the first time since 2009 and are flat in much of the rest of the country in fresh evidence of the post-Brexit vote slowdown in the property market.

The UK’s biggest tenant referencing company, Homelet, said rents on new tenancies in London fell by 1.2% in April compared with the same month a year ago, the first annualised fall in eight years.

The London average rent fell to £1,519 a month compared with £1,537 a year ago. Rents in the south-east have also fallen slightly year on year, from £1,007 to £1,003. After years of being hit by steadily rising rent bills, it appears that tenants in the capital may finally be getting the upper hand.

“Falling rents is definitely positive news for those looking to move, or to renegotiate their rents with their landlord,” said Dan Wilson Craw, director of Generation Rent, the campaign group for private renters. “Lots of residential property built over the past few years is now coming on to the market and that increase in supply is rippling through the market,” Wilson Craw explained.

Across the UK, rents in April were just 0.4% higher than a year ago, with the average monthly rent now standing at £904. Homelet added that the national level of rental price inflation has fallen to the lowest level since the depths of the financial crisis.

Research released last year showed that Londoners were spending nearly two-thirds of average income on rent, putting tenancies in the capital beyond the reach of many workers.

HomeLet’s chief executive officer, Martin Totty, said rentswere falling in parts of the country where they had previously soared, such as London. “We continue to see landlords and letting agents weighing tenant affordability considerations very seriously,” Totty said, explaining why rental inflation has slowed recently.

Rents fell in Wales, Yorkshire and the West Midlands during April but rose by 3.6% in Scotland. HomeLet’s figures tally with separate data from lettings agency Your Move, which reported a sharp fall in rents in March.

The falls in London and the south-east followed many years in which rent increases have outstripped earnings, leaving many tenants in the capital handing over 50% to 60% of their take-home pay to landlords.

Further declines in rent will put additional pressure on buy-to-let landlords to quit the market. In April, the first of a series of tax hikes came into force that will increase costs for landlords who have buy-to-let mortgages. Already there is evidence of a rapid fall in lending to landlords. The Council of Mortgage Lenders said lending in March was £21.4bn, down 19% on the year before, almost entirely due to landlords withdrawing from the market.

A double whammy of tighter Bank of England lending rules, which have forced banks and building societies to insist on greater rental cover and higher deposits, plus new taxes on rental income, has made buy-to-let far less financially attractive.

Falling rents will also pile further pressure on the many developers of luxury tower blocks who promote their apartments as investments based on the rental yield. In a bid to kickstart sales, developers are offering ever more extravagant incentives to lure buyers. One developer in north London has promised a £150,000 payment to cover stamp duty, an £18,000 electric car and free iPads to buyers willing to part with £1.99m for its luxury homes.