Tax probes into big businesses plunged by 40% over five years – triggering fears companies could dodge paying what they owe.
A series of written parliamentary questions tabled by Labour uncovered the drop in investigations by HM Revenue and Customs.
They revealed the agency's Large Business Directorate started just 1,940 enquiries in 2019/20 compared with 3,041 in 2014/15.
The amount raised from “compliance activity” on corporation tax plunged by £871million.
Campaigners urged the Government to step up inquiries so major firms stumped up cash.
Shadow Financial Secretary to the Treasury James Murray said: “Everyone should pay their fair share of tax, and so it is indefensible that the Chancellor is letting more and more of those big businesses that dodge their tax off the hook.
“We urgently need the Government to focus on making sure big firms pay their fair share of tax to support our country.”
Tax Justice UK executive director Robert Palmer said: "This fall in compliance shows the Government is going backwards on ensuring that corporations comply with their corporation tax obligations.
HMRC needs to be properly resourced so it can go out and collect the tax revenues due from companies."
An HMRC spokeswoman said: “In 2019-20, we secured more than £13bn in additional tax revenue from the largest and most complex businesses – more than ever before.
“This is money that would have gone unpaid without our intervention.
“In the same year, large businesses accounted for around 40% of the UK’s total tax revenues (£260bn).
“This covers their own tax receipts, but also tax they collected and paid to HMRC – for instance VAT and employment taxes.
“The UK tax gap for large businesses – the difference between tax due and tax actually paid – is at its smallest ever level, and is among the smallest in the world.
“At any given time, HMRC is actively investigating around half of the UK’s largest businesses.”
