Pinsent Masons warns of taxpayers losing potentially substantial amounts to HMRC unnecessarily as more than half of complaints made against the tax man were upheld.

Research by the legal firm found that, of the 58,110 HMRC complaints received to the end of March 2011, 57% of grievances from tax payers - ranging from poor treatment by HMRC staff, to errors in the amount of tax charged - found the taxman to be in the wrong by its internal complaints process.

George Gillham, legal director, Pinsent Masons said: 'Many complaints result in HMRC writing a tax liability off or offering compensation - and quite a lot of money can be at stake.'

An HMRC spokesperson said: 'HMRC serves millions of people every year, and received just under 75,000 complaints in 2011/12. We take complaints very seriously and want people to be able to tell us when we make mistakes and our service falls short.

'We have made real improvements to our customer services; 1000 additional contact centre staff are to be recruited following a £34m investment and we're turning around post faster than ever. Such improvements will reduce the level of complaints going forward.'