The real value of UK workers wages fell back to 2003 levels in 2012, following several years of pay freezes and economic restructuring, according to official figures.

After three decades of strong growth, real wages peaked in 2009, data from the Office for National Statistics shows. Since then, inflation has outstripped wage increases, leaving earnings at their lowest level in real terms in nine years.

Male full-time employees in the private sector have experienced the biggest fall in real wages, with their earnings now worth less in real terms than a decade ago.

The ONS said the fall could have a number of causes. "This may be because of pay freezes for people who remain in the same job, or it may reflect changes in the composition of jobs that people do, with some high-paid jobs being cut as the economy adjusts following the shock of 2008-09 and more low-paid jobs being created," the ONS said.

"The 'average' earnings outcome for UK employees as a whole is probably the result of a combination of pay freezes and economic restructuring."

Median gross earnings stood at £11.21 an hour in 2012, up on 2009's figure of £10.97. However, after adjusting for inflation the 2009 figure was the equivalent of £12.25 in 2012 prices, so workers saw a real terms fall. On average, workers have seen pay drop by 3% annually between 2010 and 2012.

Workers in London had higher median earnings, taking home an average of £15.54 an hour in 2012. However, they also saw incomes peak in 2009, and the 2012 figure compares with an average of £16.14 in real terms in 2002 – a drop of 4%.

Male full-time employees working in the private sector had median earnings of £12.37 an hour in 2012 – less in real terms than in 2002 when the comparable pay was £12.67 an hour.

The ONS said that although it was too early to be sure whether there has been a permanent change in the long-term trend, the decline in real wages had now been sustained for three consecutive years.

In the seven years to 2009, earnings increased at a rate of 3.7% a year in nominal terms, and thanks to low price inflation by 1.6% in real terms, continuing a trend of positive growth in real earnings every year since the late 1970s.

Since then, average nominal earnings of UK employees have remained quite flat while inflation, as measured by CPI, averaged 3.7% in the 12 months to April 2010, 2011 and 2012.

Comparing the path of real earnings in the public and private sectors the trends are similar, although the increase in the 2002-09 period was stronger in the public sector and the subsequent decline less marked. Full-time male public sector workers' real earnings averaged a decline of 2.1% a year from 2010 to 2012, compared with a decline of 3.1% a year for their private sector counterparts.

The report looked only at hourly earnings and does not reflect any changes in the number of hours workers are employed for, or an employee's total pay. A separate study published by the ONS in November suggested an increasing number of workers have been underemployed since the economic slowdown began, which combined with lower take-home pay in real terms could mean many are earning much less than they were at the start of the decade.

This data follows hot on the heels of research by the Resolution Foundation, which suggested low- to middle-income families will not see their household earnings return to pre-recession levels for another 15 years.

The TUC's general secretary, Frances O'Grady, said: "Official figures now confirm what everyone knows: living standards have been falling for the vast majority, and there is no sign of change.

"But on top of the wage squeeze, the government has been making it worse with cuts to tax credits, the freeze in child benefit and a VAT hike. Millions of low-income families – both in and out of work – are now threatened by the bedroom tax and the 1% cap on benefits. The cost of living goes ever upwards with the costs of essentials such as food, fuel and energy continuing to increase."

O'Grady said the economy would not recover until people had more money to spend. "The challenge for the government is to reverse austerity and start boosting wages and incomes for the majority. That is the only route to growth."