Rents have fallen in prime central London for every month for the past year and tenants now have the whip hand, admits Knight Frank.
Average rents are now down 4.9 per cent on a year ago, the number of new properties to let on the market has risen 29 per cent and the number of new tenancies is up 27 per cent, the agency says.
"Higher stock levels are the result of uncertainty over the short-term prospects for price growth in the sales market, which has led more vendors to let their properties" says a Knight Frank briefing.
"With more properties on the lettings market that were originally destined for sale, landlords have to increasingly ensure their properties are refurbished to a high standard to prevent void periods" warns the agency.
Demand for the super-prime market - units charging the jaw-dropping sum of £5,000 or more each week - remained strong in October, Knight Frank says, because of buyers' resistance to paying stamp duty on high-value properties for sale. Similarly, demand for properties priced below £1,500 per week remains robust, the firm says.