International law firm Pinsent Masons said the compliance yield from HMRC’s “special investigations” team hit £3.65bn in 2013/14, up from £2.97bn in 2012/13.
The company said this sum alone is equivalent to 10% of the estimated £34bn UK tax gap.
The special investigations team looks into the most financially significant and complex cases of non-compliance.
Paul Noble, tax director at Pinsent Masons, said: “These figures should be a massive jolt to anyone with undisclosed or outstanding tax liabilities that have given them significant savings.
“This increased investigatory capacity comes with a raft of other headline-hitting new HMRC powers, such as more criminal sanctions for offshore bank account holders and new accelerated payment measures.”
He added that individuals with undisclosed or outstanding tax matters should seek specialist advice “sooner rather than later”.
HMRC issued its first accelerated payment notices to suspected tax avoiders in August, and will continue to do so on a monthly basis until it has sent out over 40,000 demands.
The government body said it hopes to issue a total 43,000 notices over the next 18 months, with 33,000 going to individuals and 10,000 to businesses.
Accelerated payment notices are issued when a taxpayer has entered into a tax avoidance arrangement that has been notified to HMRC under the disclosure of tax avoidance scheme rules.
Those who receive an accelerated payment notice will have to pay the tax due within 90 days.
