Guardian News and Media/London

House prices across England and Wales rose by an average of 1.7% in 2012, according to official figures that reveal an 8.4% boom in London values but a 3.5% decline in the north-west.

Merthyr Tydfil, long a byword for industrial decline and deprivation, was the surprise table-topper in the Land Registry rankings of national price rises in 2012 with a 20.3% gain, while north-east Lincolnshire saw the greatest annual price fall, down by 9.5%.

The average price of a home in the UK rose to £162,080, but the figure masks vast regional differences.

Kingston upon Hull is the authority with the lowest average prices in England and Wales at just £68,710, down 2.1% on the year.

Meanwhile, Kensington and Chelsea in London in 2012 became the first borough to see average prices breach the £1mn barrier, rising to £1,080,479, up 13.4% on the year. But the Land Registry admitted the data is based on fewer and fewer transactions across the country.

It said sales per month across England and Wales fell to just 57,661 in the final quarter of 2012, compared to 62,073 in the same period a year earlier.

It added that transaction volumes in areas such as Merthyr Tydfil are so low the price data is especially volatile.

The Land Registry data is regarded as the most comprehensive record of price movements in England and Wales (not Scotland), with a database of 17mn sales since 1995.

Its figure of a 1.7% rise during 2012 compares to Halifax’s index, which showed a fall of 0.3% for the year, and Nationwide’s index, which said prices fell by 1%.

The month-by-month figure from Land Registry is also at odds with the two mortgage lenders.

Land Registry said prices rose by 0.8% in December, while Halifax said they were up 1.3% and Nationwide said they fell 0.1%.

Repossessions fell during 2012, the Land Registry said, and are now running at about 1,500 a month compared to 1,850 during 2011..

Average house prices in England and Wales remain 11% below the peak they reached in November 2007, just as the financial crisis was beginning to unfold with the collapse of Northern Rock. But in Greater London prices have hit one new peak after another.

The average price of a home in the capital is now £371,223 - 6% higher than in 2007. In Kensington and Chelsea prices have rocketed from £750,000 in mid-2007 to nearly £1.1mn by the end of 2012.

Meanwhile, in Nottingham the average price of £84,683 is the same as it was in 2003.

A growing number of towns and cities across England and Wales now have average prices below £100,000, including Blackpool (where prices dropped 4.6% in 2012), Darlington (down 7.4%), Hartlepool (down 4.7%), Stoke (down 1.5%), and Manchester (down 2.5%). But in Salford, the arrival of the BBC appears to have perked prices up. It saw the biggest price rise of any metropolitan district outside of London. Prices in the area rose by 6.8% to £91,508 and are now higher than the average for Manchester.

The Olympics appear to have had a mixed effect on London property prices. In Newham, the borough that hosted the games, prices rose an average of 4.6%, while in nearby Hackney prices jumped by 10.3%, the third biggest gain in the capital. But Barking and Dagenham recorded a rise of just 0.1% to £210,944, while Redbridge, another east London borough, was the only part of the city to witness a price fall, down by 0.2% over the year.