It believes the quality of its customer service “could be considered a genuine threat to tax collection”.
In the first half of 2015, HMRC contact centres answered only half of calls, and only 39 per cent within five minutes.
HMRC responded that it had now recruited 3,000 more staff but that the customer service issues had not affected its ability to collect tax.
Meg Hillier, chair of the PAC, told the BBC that HMRC must “rapidly improve its customer service, previously described by the PAC as abysmal and now even worse”. In 2014, 72% of calls had been answered.
The PAC also said that the failure to gather intelligence on losses from tax avoidance was an obstacle to improved tax laws.
It also described HMRC’s record of 11 prosecutions for offshore tax evasion in the past five years as “woefully inadequate”.
Despite being handed a list of 3,600 British people who hid money in Switzerland, the tax collectors have prosecuted just one person involved.
Instead, the tax collectors have offered reduced penalties to people who come forward with information about money they’ve hidden overseas, something the committee says is no substitute for the “deterrent effect” of prosecution.
In response, HMRC pointed to its record results and said the gap between tax due and tax collected had been reduced to one of the lowest in the world.
“We are disappointed that the Public Accounts Committee has overlooked HMRC’s record results, which include collecting a record £517bn in tax revenues,” an HMRC spokesperson said.
The PCS union blamed the problem on 11,000 full-time equivalent posts being cut since 2010.
“It has been abundantly clear for years that the department has cut too many staff and that services are suffering,” its general secretary Mark Serwotka said.
“The department needs major investment backed by a real political commitment to tackle tax evasion and avoidance as an alternative to more damaging spending cuts.”
