A survey by the Resolution Foundation ‘think tank’ has found that real wages have fallen further than official figures show since the beginning of the financial crisis — because the Office for National Statistics does not include wage growth among the self-employed.

If it did, the fall of 10% in average wages since 2008 would increase to more than 12%.

The self-employed now account for one in seven of the UK workforce — or 4.5 million workers — and they have suffered a 27% fall in their income. Laura Gardiner — a senior analyst at the Resolution Foundation — said official figures used by the Bank of the England give “a picture that’s incomplete at best and sometimes misleading.

What we know about earnings is central to our understanding of the recovery and the timing of interest-rate rises, so it is crucial that we equip ourselves with the best possible wage measure.”

The Bank’s Monetary Policy Committee is expected to raise interest rates before the end of 2014, despite concern among business groups that wages remain well below their peak and pay awards remain low.