Sub-prime mortgages are more common in the west of Scotland than in the rest of the country, official figures have revealed.

With the world suffering a financial crisis sparked by a collapse in sub-prime lending in the USA, details of the pattern of the practice across Scotland have been released.

Lanarkshire and Ayrshire have the highest percentage of home loans to people with impaired credit ratings.

Both areas have had a combined total of more than 5000 impaired credit mortgages in the last three years, accounting for up to one-quarter of all sub-prime loans in Scotland.

Since April 2005, of 630,000 mortgages arranged in Scotland, 21,130 were sold to people with an impaired credit history. Many more with a low credit rating also fall into the sub-prime category, but no figures are kept for them.

The extent of sub-prime mortgage approvals was revealed by Communities Minister Stewart Maxwell in response to a question by west of Scotland nationalist MSP Stuart McMillan who said banks had to take responsibility for their lending policies. North Lanarkshire had the highest impaired rate with 4.4% of a total 39,309 mortgages, followed by East, South and North Ayrshire, all on 4.3%, and South Lanarkshire with 4.1%.

Glasgow had 3.5%, roughly in line with the Scottish average of 3.4%, while the areas with traditionally the highest house prices, Aberdeen and Edinburgh, were well below at 2.6% and 2.7% respectively.

Mr McMillan said: "Up until a few months ago we had not heard of sub-prime mortgage far less know how many people fell into that category. I think lenders have been too open and relaxed in giving out mortgages.

"Hopefully these people can still meet their repayments, but they are among the most vulnerable. If they were to hit trouble it would mean more than 20,000 families losing their homes. That is not only a disaster for them, but will cause serious problems for local authorities who provide housing."

Towns in Lanarkshire and Ayrshire have seen a huge rise in prices in recent years. Kilmarnock went from almost zero growth in 2005 to an increase of 35% the following year. One leading Ayrshire estate agent said: "Where a tenement flat would have cost £40,000 a few years back, it will now be on the market for £90,000.

"The M77 has helped, but also a lot of former local authority houses were bought, which then came back to the market at higher prices. We were many years behind Glasgow in this respect.

"Whether that has led to more sub-prime borrowing I don't know, we haven't yet seen an increase in repossessions. That could follow if people have borrowed a lot to meet rising prices."

With the cost of mortgages increasing, financial experts believe more people will be unable to afford their mortgage repayments - with those in the sub-prime category the most vulnerable.

Recent figures from the Council of Mortgage Lenders showed lenders repossessed 18,900 homes in the UK in the first half of this year, the highest number for 12 years.

Mr Maxwell said: "The Scottish Government would discourage borrowers from taking on unsustainable mortgages and to seek help from their lender if they are having trouble repaying."