St Albans properties are among the most expensive per square metre in England and Wales, new analysis has revealed.

With an average property value per square metre of £5,582, the city has been named the tenth most expensive location in a new Rightmove countdown.

West London topped the list with £10,427, and was followed by five other areas of London, plus Harrow, Twickenham and Kingston Upon Thames. The cheapest place per square metre is the SR postcode in Sunderland (£1,417).

The average asking price per square metre of a house in England and Wales is £2,954, up 19 per cent (£2,487) on five years ago and 0.8 per cent on this time last year (£2,930).

Rightmove have used this data to create a new House Extension Cost calculator, which estimates how much extensions could add to the value of a house, along with estimated labour costs, in 103 postcodes across England and Wales.

It includes potential values for a small (15m2 ), medium (25m2 ) and large extension (35m2 ).

According to the calculator, a small extension in the AL1 area of St Albans would involve labour costs of between £16,182 and £18,807, resulting in a potential increase in property value of between £77,453 and £90,013.

Tim Bannister, director of data services at Rightmove, noted this was "a very rough guide", adding that homeowners first need to think about why they are doing an extension.

He said: "If it's to add value to a home then it's worth bearing in mind that local markets all differ, as does the price that people will be able to pay for a property, so there will be times where adding an extension will not increase the home's value by more than its cost.

"But for many people the reason is so that they can have more space at that moment in time, and so adding some value for when they do go on to sell in the future could be a bonus for them.

"The final cost will depend on the materials that homeowners might need to buy as well as any extras such as planning permission. The key thing, however, is to be clear on how much you can afford to spend and to make sure you have a contingency pot as well."