HM Revenue and Customs (HMRC) has issued an apology following a temporary shutdown of its helplines on Thursday, just weeks before the crucial self-assessment deadline at the end of January.

The telephone services were suspended at 11.40am owing to a brief technical glitch, the tax authority confirmed, though all lines were restored by 2.15pm. HMRC urged taxpayers to utilise its online platforms wherever feasible.

An HMRC spokesperson said: "We've now reopened our helplines – including for self-assessment. We thank people for their patience and are sorry for the inconvenience."

The disruption occurred as the self-assessment deadline of January 31 draws near. Those failing to meet the cut-off date risk an immediate late filing charge of £100, with the possibility of additional penalties thereafter.

Data published by HMRC on January 5 revealed that over 6.36 million taxpayers had already lodged their tax returns by that point, whilst nearly 5.65 million remained outstanding ahead of the deadline.

Jenny Ross, Which? Money editor, said: "With the self-assessment tax deadline rapidly approaching, it's hugely concerning to see that HMRC's phone lines have gone down. This will be hugely frustrating to those needing help with their tax returns, and particularly disruptive to those unable to use digital services."

Taxpayers who cannot submit their self-assessment returns on time have been previously advised to notify HMRC before January 31. HMRC has stated it will handle cases with legitimate reasons sympathetically.