Her Majesty’s Revenue and Customs (HMRC) has been forced to apologise for "shocking" customer service that has hit small businesses struggling to complete their tax forms.

A parliamentary answer to Richard Burden, the Labour MP for Birmingham Northfield, showed that barely one-third of telephone calls made to HMRC contact centres were handled within five minutes in the second quarter of the last financial year, and only 40.3 per cent between April and June 2014.

Both figures were substantially down on the same periods in the 2013-14 tax year, while a quarter of calls were not being answered at all over those six months.

Unions have complained that swingeing cuts at HMRC, which included shutting 14 offices and inviting nearly 700 staff to take voluntary redundancy last year, would hurt the service. Small business owners often struggle with the UK’s complicated tax and accounting systems. They frequently need advice but can face fines if they make a mistake having been unable to speak to a specialist.

When The Independent put the figures to HMRC, a spokesman said: “We’re sorry that some customers are struggling to get through”. He added that plans were in place to “improve our performance” and that 3,500 more staff would soon be placed in customer service roles.

Mr Burden said the statistics were “shocking” and that he had written to the Paymaster General, Matthew Hancock, warning that the focus on “digital reform” – so that more administrative work is done online – is hurting those with limited computer access.

He claimed there was a widening “digital divide” and pointed out that a “frustrated” 93-year-old constituent was on hold for more than 20 minutes on two occasions, which was then followed by problems receiving forms vital to completing his self-assessment tax document.

John Allan, chairman of the Federation of Small Businesses, said: “Small firms often find themselves wrestling with highly complex tax issues and many need help to navigate the system. This can be highly stressful and confusing. Getting it wrong may lead to costly fines and time-consuming investigations.

“The recent evidence of poor performance by HMRC’s telephone contact centre is therefore disappointing. HMRC must do more to make sure... that service levels are raised significantly.”