One of Britain's biggest trade unions has demanded an investigation into the mass shifting of City bonus payments into April to take advantage of the 5p cut in the 50p top rate of tax by the Chancellor, George Osborne.
The Unite union has written to HM Revenue & Customs describing the practice as a "scam" and calling it a "conscious and deliberate" move to avoid tax.
The 50p rate was charged on earnings above £150,000 a year but was reduced to 45p in April.
Unite wants the Revenue to investigate whether delaying bonus payments until the cut came into force – which it says could have cost the Government more than £65m in revenues – broke the law.
It cites figures from the Office for National Statistics showing a spike of £700m in bonuses in April when the tax cut was introduced compared with when they might usually be paid between December and March.
The reduction to the top rate has been described as "the millionaire's tax cut" by opposition politicians.