It's been well publicised lately that the housing market is on the brink of a crisis - in fact, the crisis has hit the US already. As mortgages become harder to come by and homeowners begin to struggle with rising interest rates and lower demand from buyers, the market is faced with a vicious circle in which prices keep falling, but there are not enough mortgages being offered to increase demand.

What happened? - a timeline

The problems can be traced back to the housing market in the US, in which people with poor credit history (known as 'sub-prime' borrowers) were allowed to take out mortgages - many of whom subsequently could not keep up with payments.

Many of these mortgage debts had been 'bought' by UK banks, meaning they were now responsible for receiving the repayments. However, due to the amount of times these debts had been bought and resold, it was often difficult for banks to predict how much of the debts would be repaid.

When many of these sub-prime borrowers began to fall behind on repayments, it hit whoever 'owned' the mortgage debts - meaning both the US and the UK were affected. This is what became known as the 'sub-prime mortgage crisis'.

What is happening now?

UK banks' losses have in fact been small so far - but there is a risk that they could get a lot bigger. For this reason, they are very cautious about new lending, and so they are tightening the criteria needed to qualify for mortgages.

The knock-on effect of this is that houses are harder to sell, meaning prices are getting lower. However, lower mortgage availability means that demand isn't getting any higher - so house prices are likely to fall further - and so the cycle continues.

The Bank of England has acted on two fronts. Most significantly, they have swapped £50bn of secure Government Bonds in return for banks' mortgage debts - effectively a show of confidence that sub-prime losses will not be as big as the banks feared. This move is designed to calm the insecurity that is causing the tighter lending policies and prevent any particularly dangerous drops in house prices.

Additionally, they have lowered the basic interest rate in order to convince banks to lower mortgage interest rates - but this is currently not working, and so the problems continue.

What happens next?

There are mixed opinions amongst the experts:

RICS (Royal Institute of Chartered Surveyors)

·Predict that house prices at the end of 2008 will be down by 5

CML (Council of Mortgage Lenders)

·House prices at the end of 2008 will be down by 7 to 770,000 sales

Although the extent of the predictions vary, nearly all experts agree that the housing market is increasingly on the downturn. House prices have only fallen slightly so far - but if the trend continues, the housing market will decrease in value significantly in the coming months.

The US have already been through what the UK is going through now - a tightening in lending criteria combined with fewer mortgages - and they have seen some sharp falls in house prices. Many economists believe the UK will follow this pattern.

Banks need to continue borrowing and lending, if a little more carefully than before, if the market is to recover. If they don't, house prices will continue to fall, and it could be years before they begin to rise again.