HMRC has announced it will tax the 'loyalty bonuses' paid by investment fund supermarkets from the start of the next tax year, 12 months earlier than expected.

HMRC has ruled that the payments, whereby some fund-selling websites pass on part of their renewal advice commission on certain funds to investors, are now classed as 'annual payments' and should therefore be taxed as income, starting on 6 April.

This means that the 20% basic rate tax will be deducted from the bonuses at source and higher-rate taxpayers will need to declare and pay additional amounts on annual self-assessment forms.

Hargreaves Lansdown, the largest payer of loyalty bonuses on funds in the UK, called the decision 'anti-competitive' and said it was a 'worrying precedent' that could spread to other forms of cashback, such as those on supermarket loyalty schemes and credit cards.

The Financial Services Authority (FSA) has said it wants to ban such 'trail commission' payments to fund supermarkets in 2014 and is expected to announce the details next month.

Ian Gorham, chief executive of Hargreaves Lansdown, said: 'The discount tax is not good news for investors, businesses or the Government and joins the likes of other unpopular taxes such as the granny tax or pasty tax.'

In a statement, HMRC said claims that cashback in other industries could be targeted next were 'complete rubbish'.

A spokesman for HMRC said: 'Tax will be due from April onwards on all commission paid by investment funds to investors. We will not collect tax on earlier years commission. "Until the end of 2013 to allow the rules to bed in we will accept an estimate of tax deducted at source. We will work very closely with stakeholders to ensure the rules are applied fairly across the board.'