I only pay 13 per cent tax on my fortune, admits Romney

Mitt Romney bowed to increasing political pressure today by releasing his tax returns and revealing his vast wealth.

The disclosure will spark controversy because it shows the multi-millionaire pays a lower tax rate than most Americans. Because much of his earnings are from capital gains on investments rather than earned income, the 64-year-old enjoys substantial tax breaks - in 2010 he paid just 13.9 per cent, or $6.2 million, on a total of $42.5 million. In comparison, his rival for the Republican nomination Newt Gingrich paid $1million at a rate of 31 per cent.

The figures will not sit well with a squeezed US middle class which increasingly feels the super-rich were let off during the credit crunch and will prosper again now the economy is recovering.

But during the first debate since Mr Gingrich scored a shock win in South Carolina, Mr Romney hit back, saying: "I'm proud of the fact that I pay a lot of taxes." Mr Romney's team believe Mr Gingrich's personal attacks on their man lost him the South Carolina vote and will now adopt a similar tactic.

Mr Romney claimed Mr Gingrich had "resigned in disgrace" from Congress after four years as Speaker and then had spent the next 15 years "working as an influence peddler".

Tonight President Barack Obama makes his annual State of the Union speech to Congress. He will pile the pressure on Mr Romney, one of the richest men to run for the White House, by urging higher taxes on the wealthy.