National debt has increased steeply since the rescue of Northern Rock
Government debt rose to £750.3bn in 2008, more than half of gross domestic product (GDP), according to the Office for National Statistics (ONS).
The ONS data also showed that the government's deficit, as defined by the EU's Maastricht Treaty, more than doubled to £78bn from £36.7bn.
It means that government net borrowing is the equivalent of 5.4% of GDP.
The Maastricht Treaty specifies that deficits should not exceed 3% of GDP and debt should not exceed 60% of GDP.
Last week, the European Commission set deadlines for five countries, including the UK, to rein in their budget deficits.
The UK was given until 2013-14 to reduce its deficit to meet the 3% target.
The debt figure includes the government's rescue of Northern Rock, which was nationalised in February 2008.
It does not include subsequent bank bail-outs or treasury bills provided to the Bank of England for use in the Special Liquidity Scheme since April 2008.