A strike by tax call centre staff has given a 48-hour reprieve to taxpayers facing a £100 fine for late online filing of their self-assessment return.

HM Revenue and Customs has extended the deadline from midnight tonight to midnight on Thursday.

Anyone ringing HMRC today is warned about the strike and told they face delays.

Callers are also told about the two day extension, promising that anyone filing online by the new deadline will be treated as though they filed it by the original date.

Kent-based accounting firm McBrides welcomed the extension. Nick Paterno, managing partner, said: "It's good to see that the Revenue are being reasonable about this and not inflicting further penalties on the taxpayer as a result of internal industrial action."

As many as 7,000 HMRC call-centre staff are expected to walk out today in a dispute with the Public and Commercial Services Union.

Mr Paterno added: "Although online filing of tax returns should not be affected, a shortage of staff on the helpline means people who have left their tax return to the last minute could find difficulty getting the right advice."

More than half a million people were expected to file their returns today.