As many as 100,000 workers are currently facing uncertainty after a leaked e-mail from HM Revenue & Customs showed that their final bills for last year may have been miscalculated.

The private exchange between HM Revenue & Customs employees shows that those who underpaid or overpaid income tax last year may still have paid the wrong amount, newspaper The Telegraph.reports.

The majority have already been sent new calculations or have been issued with refunds, however all will now have their liabilities recalculated yet again.

HM Revenue & Customs estimates that fewer than 100,000 people would be affected by the new mistakes, but did admit that it did not know the extent of the problem.

In a precautionary move, HM Revenue & Customs has ceased sending repayments until the problems are resolved.

In the summer, HM Revenue & Customs admitted it had collected an incorrect amount of tax from more than five million people in the 12 months to April 2014.

Since then, the taxman has sent those affected notification letters explaining how it would attempt to get back or issue refunds for on average £300.