UK house prices London housing
UK house prices are rising sharply again, but how long can this carry on, particularly in London?Getty

House price growth is booming again in the UK and values will keep on rising as the economy grows strongly, according to Halifax.

The mortgage lender said its house price index was up 9.7% over the year in October 2015, which took the average price of a home to £205,240.

"Improving economic conditions and household finances, together with sustained low mortgage rates, have boosted housing demand during 2015," said Martin Ellis, Halifax's housing economist.

"Strengthening demand is filtering through into higher sales levels, although the ongoing shortage of supply is acting as a significant constraint on activity. The imbalance between supply and demand is likely to persist over the coming months, maintaining upward pressure on house prices."

But is this all good news? Probably not, if you're an aspiring first-time buyer, and maybe not if you bought a house recently. Here are reasons to be concerned about the current state of the housing market.

Share prices of important estate agencies are falling

There's a clear sign that investors are losing confidence in the momentum of the housing market because the share prices of some well-known real estate agencies are dropping. Property experts were expecting a strong rebound in housing market activity after the general election, but it is weaker than expected.

Countrywide, which owns the Bairstow Eves chain of estate agents as well as a large mortgage brokerage, has lost 29% in the value of its share price since mid-June 2015 -- and it just issued a profit warning.

The high-end estate agency Foxtons has seen 32% clipped from its share price since 1 June as its profits fall. LSL Property Services, which owns the Your Move and Reeds Rain estate agencies, has clipped 15% off its share price since June 23.

"Every time there is an election, the property market slows down, then there is a bounce afterwards," Jim Clarke, the chief financial officer of Countrywide, told The Times. "This is the first time since 1983 that it has not happened."

Two major investment banks have sounded the alarm on London

Both UBS and Deutsche Bank have put out reports suggesting that London's rampant property market had peaked. House prices in the capital average a whopping £522,000, according to the Office for National Statistics.

UBS has warned that a substantial price correction could be in the offing because house prices ran so far away from earnings in the city, where a serious shortage of supply and intense demand from residents and speculative investors forced up property values.

"London is by far the most overvalued market in Europe, at risk of a bubble as a result of explosive price behaviour since 2013," the UBS report said.

Similarly, Deutsche Bank warned that too many buyers expected prices to continue rising, which was obviously impossible, so they were willing to pay more than was rational to buy property.

If this attitude suddenly changes, the bottom could fall out of the London market. And it could change amid the increasing politicisation of the housing issue and a tighter grip on the mortgage market by the Bank of England.

As the report's author Sahil Mahtani put it: "Perhaps we are close to the turning point. Valuations are high relative to history, falling interest rates cannot provide further support, and given current affordability home ownership cannot rise materially. London's property is unlikely to enjoy the next 30 years as it did the last."

City house prices may have peaked

Hometrack, a housing market data firm, said house prices in 20 of the UK's biggest cities grew on average by 8.4% over the year to September 2015, up from 6.6% in May. But the three-month change was much slower at 3.7%.

Hometrack said 13 of the 20 cities saw growth slow in the three months to the end of September, a sign that price growth had peaked.

"It is important not to read too much into one month's headline results, but there are signs that the pace of city level house price growth is likely to continue slowing," said Richard Donnell, director of research at Hometrack.

"There has been a surge of demand since the election in May but weaker mortgage approvals and evidence from survey data suggests less frenetic demand in the final quarter of the year."

Mortgages are about to become more expensive

In August, there were 71,030 mortgage approvals, according to Bank of England data, after the strongest monthly rise since the worst of the financial crisis in 2008.

Approvals are averaging around 70,000 a month, well above the lows of the crisis but slightly lower than levels seen in 2014. And the number of residential property transactions hit 294,190 in the third quarter of 2015, well up from their nadir in the first quarter of 2009, when the figure was 120,460.

This is supported by the Bank of England's record-low base rate of 0.5%, which has kept mortgage costs low – allowing people to service the larger debt they need to pay for higher house prices, particularly in London. But the economy is recovering strongly and rates will soon rise, pushing up mortgage costs.

Russell Quirk, the chief executive of eMoov.co.uk, said: "We as a nation should learn from previous property lessons and proceed with caution. Yes mortgage costs are low at present, but this won't be the case forever. I think a large number of the British public scrambling to secure mortgages now, coupled with a severe lack of stock on the market, is a dangerous fuel to be driving the property market on.

"UK buyers could be tempted to borrow more than they would in normal circumstances, in order to secure a property in a market where it is becoming increasingly difficult. Should interest rates jump up, they could find themselves in a difficult situation financially."

Housing starts are falling again

The government has made much of its attempts to kickstart housebuilding in the country, which has been running at around half the level needed to meet current demand.

The Town and Country Planning Association thinks the UK needs 1.5 million new homes in just five years. In London and the south east, a protracted shortage of housing supply has driven up house prices. But housing starts have started falling.

According to the latest government figures for England, housing starts fell by 14% in the April to June quarter, to 33,280. And that is down 6% over the year. The only sustainable solution to the housing crunch is to build more houses, so any drop in the number being started is a concern.