HM Revenue and Customs (HMRC) seems to "lose its nerve" when faced with the prospect of taking legal action against global giants, said Commons Public Accounts Committee.
They also claim HMRC has fallen short on the unpaid tax it hoped to extract from Swiss bank accounts - collecting just £440 million so far this financial year, rather than the £3.12 billion forecast after a bilateral agreement.
Changes in "controlled foreign company" rules and the failure to close a loophole relating to Eurobonds have made it "easier for the companies to avoid tax, while ordinary people continue to pay their share," said the committee's chairman Margaret Hodge.In comments which will raise questions over the Treasury's intention of using a clampdown on tax evasion and avoidance to plug holes in the public finances, the committee noted the planned income from the Swiss accounts were written into Chancellor George Osborne's budget estimates in last year's Autumn Statement.
They said it was "astonished" at HMRC's failure to account for the shortfall.
Ms Hodge said: "In pursuing unpaid tax, HMRC has not clearly demonstrated that it is on the side of the majority of taxpayers who pay their taxes in full.
HMRC rejected the findings, saying MPs been selective and misleading.