The government has sent out 70 different kinds of ‘intervention’ letter, detailing common mistakes in tax filings that individuals may have made.

The letters are intended to resolve problems without opening costly enquiries, but have dismayed some, who have argued that HMRC should stick to established legal procedures.

An example letter provided by HMRC suggests taxpayers look again at their arrangements and re-file returns: ‘I am not suggesting that you have made errors but I would like you to review your declarations made within the past 12 months and let me have, by (insert date), details of how any such (disposals/transactions) were dealt with together with: confirmation that your declarations are correct; or a schedule of disposals/transactions) along with your revised figure for (tax type), in order that I can recalculate your tax liabilities,’ .

Anne Redston, who has seen the letters, said that some directed taxpayers to HMRC manuals, which due to their complexity would be unlikely to be enlightening.

An HMRC spokesman said the trials of such letters were ‘small-scale’ and and ‘entirely voluntary’.

‘In order to improve the way we work, we are trialling new, simpler and less time-consuming ways of helping our customers.’