According to Saffery Champness, HMRC handled a total of 81,066 complaints in 2015/16, over 7,000 more than the previous year (73,646) and an increase of more than 16,000 on 2013/14 (64,313).
This is the closest the figure has gotten to the record high level of 83,917 complaints in 2008/09 during the financial crisis.
The volume of complaints upheld also increased steadily from 2008/09 to 2015/16 with over half of complaints partially and fully upheld last year, compared to 37% in 2012/13.
Lucy Brennan, partner at Saffery Champness
As HMRC has sought to get to grips with its new strategy, many taxpayer services have been withdrawn
The increase in complaints being upheld could either be due to improved systems and processes uncovering errors and anomalies or HMRC looking to tie up matters swiftly and avoid lengthy and complex appeals for its overstretched staff, Saffery Champness said.
The accountancy firm also highlighted that the spike in complaints coincided with HMRC’s launch of Making Tax Digital in 2015.
Concerns have been raised about HMRC’s ability to deal with the large volumes of complaints regarding the implementation of Making Tax Digital.
The Revenue has faced repeated criticism over service standards as call-waiting times increased dramatically last year following a raft of staff cuts.
James Hender, partner and head of the private wealth group at Saffery Champness, said the UK tax authority “has bitten off more than it can chew”.
“By cutting back resources and rolling out a complex digital system at the same time, taxpayers and businesses have been left with real concerns and grievances; the numbers speak for themselves,” he said.
Hender added that the firm's clients are “acutely aware that HMRC can have a poor response time and that it does not have sufficient resources to enable it to deal effectively with the more complex investigations”.
Hender said suspicions could be raised that “frontline staff are being dragged away from their day jobs to deal with the ever growing mountain of complaints received”.
Lucy Brennan, partner at Saffery Champness, agreed that HMRC’s digital drive is “clearly suffering from significant growing pains”.
“Over three million taxpayers used an online personal tax account this year and, with HMRC aiming to go fully digital by 2020, more and more people are coming into contact with the new digital services and are inevitably coming up against obstacles,” she warned.
Brennan also highlighted the struggles taxpayers are facing as they try to adapt.
“As HMRC has sought to get to grips with its new strategy, many taxpayer services have been withdrawn, guidance on key issues such as on non-dom policy has been largely absent and Making Tax Digital itself has already faced significant delays."
“Ironically, there is also the possibility that in seeking such large quantities of data, the administrative costs of the rising number of complaints and investigations will cost HMRC more, rather than raising additional revenue more efficiently,” she added.
A report by the Public Accounts Committee published in July warned that further spending cuts to HMRC could hit taxpayers by triggering a further collapse in service standards.
The report revealed that the Revenue's helplines cost customers £1 for every £4 saved, with people waiting for their calls to be answered for 47 minutes on average.
In addition, more than a quarter of people gave up on their calls due to the “unacceptable” waiting times.
HMRC announced a major reorganisation in September, streamlining its internal structure to improve its customer service standards and help ensure a smooth digital transformation.
In a briefing note to staff, HMRC chief executive Jon Thompson said that the move will “deepen our specialist skills and knowledge, and will help us to respond more flexibly and speedily to changing business and customer needs.
He added, “It will also make it easier to do things consistently, for example, establish our once-and-done approach across all our interactions with customers.
“Having fewer groups – whose responsibilities are clearly defined – will make it easier for both colleagues and customers to know who to talk to.”
Denying that there was any link between Making Tax Digital and the volume of complaints, a spokesperson for HMRC said, “We apologise to the customers that we have let down.
"We take complaints very seriously, we want people to tell us when we make mistakes or our service falls short so we can improve our systems and services.”
The spokesperson added that HMRC is turning around complaints more quickly than ever before and expects to see a drop in the numbers in 16/17.
The Revenue is also piloting a complaints "iForm" with personal taxpayers – allowing customers to complain online for the first time.