At the top end of the property ladder, particularly in London and the South East, there is no sign of the gloom beginning to grip other areas of the UK housing market, according to Savills, the high-class estate agent and commercial consultant.

It said today that the "prime" and "super-prime" property markets, buoyed by bumper City bonuses and wealthy international investors, continued to flourish.

It added that rates of sales and properties under offer were "ahead of last year".

Later today, Savills is going to sealed bids with the sale of a six-bedroom Georgian townhouse in Alexander Square, South Kensington.

The house was on the market at £7.5 million but is expected to go for significantly more than the asking price, with 12 buyers preparing to bid.

A spokesman for Savills also reported that it sold a house recently on Cheyne Walk in Chelsea.

The guide price was £8 million, he said, but a buyer walked in off the street and asked how much he would have to offer for the property to have it taken off the market.

Savills, which also markets and manages commercial properties, added in a trading update for investors today that the prime residential markets it specialises in should be little affected by any future rate rises.

This comes in the face of a "cooling" in the UK mainstream residential market after four interest rate rises since August.

Savills is regularly seen as a barometer for sentiment at the top end of the property market and is associated with new developments such as at London's 1 Holland Park, where new apartment blocks are regularly sold in advance of being built.

"New homes markets in certain provincial cities are starting to show signs of oversupply, but markets in London and the South East remain strong," Savills said.

"Super-prime markets have continued to rise strongly, due in part to interest from international purchasers."

The comments add fuel to worries that a two-tier market has developed, reinforcing a North-South divide where super-wealthy investors are immune to any of the macroeconomic tensions that effect the less well-off.

The Halifax noted in its monthly survey today that house prices in the North of England had broken through the £150,000 barrier for the first time.

Savills said that commercial investors were still hunting for prime properties across Europe but were becoming increasingly selective in their hunt for the best rental yields.

It added that it was confident of a "good result for 2007". The shares rose 1p to 602.5p.