The warning comes as data from national Citizens Advice highlights how frustrated callers tweeted HMRC over 11,500 times in the last 12 months to complain about long phone line queues.
The new analysis also shows people complained via Twitter about spending an average of 47 minutes in total to speak to someone at HMRC.
While official figures suggest an average wait of 10 minutes, the study from Citizens Advice shows many people are waiting longer. One person tweeted they had tried to get through to HMRC on four occasions - waiting an hour each time.
Reasons for calling HMRC include explaining a change in circumstances that will impact on tax credits, for example losing their job or having a child, or to clarify income tax payments.
Citizens Advice carried out the study, which looked at complaints made to the @HMRCgovuk Twitter account between September 2014 to August 2015, after people seeking help from local Citizens Advice reported not being able to get through to resolve matters with HMRC.
Citizens Advice advisers acting on behalf of clients also face long queues for the intermediary line, which organisations like Citizens Advice can use to make direct contact with HMRC staff.
Richard Wilkinson – Chief Executive of Citizens Advice Bolton said: “Time and time again we are seeing people who know they need to update HMRC on their tax or circumstances but are really struggling to get through on the phone.
“If a person can’t update HMRC about their tax credit circumstances they may not get all of the support available or instead are overpaid which can cause debts further down the line.
“Similarly a worker may not be able to file their self assessment return on time if they cannot get through on the phone to ask a question, and could face a fine for missing the deadline.
“With Citizens Advice staff and volunteers also facing similar queues it is important HMRC urgently addresses the problems many people are experiencing with phone lines.”
HMRC phones lines are 0300 numbers meaning calls are charged at the same rate as a standard landline call and could be included in some phone package’s free minutes. However if a person is waiting 47 minutes it could cost them £4.66.
The charity is also warning that the roll-out of Universal Credit and changes to tax credits could mean waiting times will further soar as more and more people try to speak to someone about their circumstances.
Peak months for complaints via Twitter include:
- January 2015 when income tax self-assessments are due by the end of the month (1,133 tweets).
- June and July in the run up to the 31 July deadline for tax credit renewals (1,443 for June and 1,128 for July).