High end estate agents and mortgage brokers in London's post postcodes have seen their business bruised by a drop in sales of £1m-plus properties.

The number of home sales worth at least a million pounds across Great Britain has declined to its lowest level since 2009, according to new research by Lloyds TSB.

There were just 3,043 £1m-plus property sales in the first half of 2012, says the lender. This is the smallest total since the first half of 2009 and a significant 11% lower than in the same period in 2011.

Sales of these premium properties are hugely underperforming the wider housing market, which isn't exactly galloping ahead, but has seen a 3% rise in sales.

This is the opposite of last year's trend when it was the mansions significantly outselling average homes on the wider market.

Suren Thiru, a housing economist at Lloyds TSB, says: "The number of homes sold for over £1m has fallen significantly over the past year, reversing the increases recorded over recent years.

"This partly reflects the changing market conditions for those looking to buy such properties including the 40% increase in the Stamp Duty rate for multi-million pound homes."

Capital losses
London accounts for nearly half of the national decline in £1m-plus property sales, seeing a 7% drop in transactions between the first half of this year and last year.

But despite the fall, two thirds of all sales over £1m in Great Britain were unsurprisingly still in the capital. In fact, a quarter of them were in the London local authority districts of Kensington & Chelsea and Westminster.

Across the country, sales of homes worth at least £2m also fell over the last year, by 10%, partly due to the introduction of a 7% Stamp Duty tier on properties above £2m (and 15% for some corporate buyers).

Jonathan Harris, director of Mayfair-based broker Anderson Harris, arranges finances for high-net worth property buyers, and has witnessed a noticeable slump in £2m-plus sales:

"There has definitely been a decline in sales in £2m-plus homes as the Stamp Duty changes have a catastrophic effect on that price bracket. The new phenomenon is the purchase price of £1,999,999 for properties that would normally have been marketed for £2.5m."

Growth in mega mansion sales
There is one part of the premium property market that is still booming - homes over £5m. Sales of these uber-posh pads have continued to increase, rising by 5% to 81 in the first six months of 2012 – the third successive annual increase.

Lloyds TSB's Thiru explains: "There does remain a certain amount of strength at the very top end of the housing market with sales of homes worth more than £5m continuing to outstrip the rest of the market, with the very top end of London property market still seen as a 'safe haven' by investors."

Harris agrees that the super-rich are not troubled by the increased tax burdens on premium property transactions. He says:

"Overseas borrowers are still prevalent in the prime central London market, buying for well over the £2m-mark. UK buyers would always have been more likely to buy in the £1m-£2.5m bracket, and they are the ones who have been put off by Stamp Duty.

"The top end of the market - £5m-plus - is largely insulated from changes in tax rules as you are talking about really wealthy buyers. The overseas buyers whose home countries are suffering economic or political turbulence, such as Russia and Syria, are so desperate to buy in a safe haven like London that the Stamp Duty almost doesn't matter.

"The Russians continue to buy in a company name even though they have to pay 15% Stamp Duty to do so; it's the anonymity which is important to them more than anything else."

The top end of the London market is clearly well insulated, but what about sales of premium properties in the rest of Great Britain?

Mansion hotspots
While sales of £1m-plus homes may be relatively common in the capital (accounting for over one in 20 sales) in the rest of the country they are rare, accounting for just 1% of total property sales in the first six months of 2012.

In fact over half of all local authorities haven't seen even one sale of a £1m-plus property in the last year.

After London, the bulk of million pound plus home sales were unsurprisingly in the South East, followed by the East of England, then the South West.

The biggest hotspot outside of the South of England is Scotland, accounting for 1.7% of all sales, where 60 premium properties have changed hands in the first six months of this year, a third of which were in Edinburgh.

Below is a list of the home sales over £1m across Great Britain in the first half of 2012, sorted by region:

London - 2034
South East - 578
East of England - 180
South West - 98
Scotland - 51
North West - 34
Yorkshire and the Humber - 22
West Midlands - 22
East Midlands - 19
North East - 4
Wales - 1
Great Britain - 3043

Source: HM Land Registry and the Registers of Scotland