Rightmove is also seeing evidence that house price growth in London is no longer being driven by the wealthy "prime central" boroughs.
London's worst-performing borough in March was named as Kensington and Chelsea, where asking prices had dropped by 2.4% on the previous month.
But the average price tag for a home in the borough was still £2.1 million.
The English capital's best-performing borough was found to be Haringey, where prices had surged by 9.5% month-on-month to reach £597,634 typically.
Westminster and Camden, where average asking prices were above £1 million, were also among Rightmove's worst-performing areas in London in March, while Barnet and Hounslow, where prices were around £600,000-plus, were among the best.