The UK Government has a credibility problem when it comes to tax avoidance.

While George Osborne insists he is closing tax loopholes and bringing in anti-avoidance measures which could save £6.8 billion, doubts about the Chancellor's sincerity remain.

The European Commission and the OECD both fear some UK law amounts to "harmful" tax practices. One example is the patent box law, which grants companies tax breaks in relation to patents, even when the income being claimed against has no direct relation to the patent concerned. The UK is also strangely tolerant of companies which come here solely to claim tax breaks. Notionally, such firms are allowed to keep money which would otherwise be due to the state, in order to encourage them to invest in growth or jobs. However, many simply bank the proceeds and do not invest at all.

The Public Accounts Committee - one of Westminster's more effective bodies for holding ministers to account - has further undermined the Government's credibility over tax avoidance with a new report.

It points out the external concerns about such UK policies and highlights some of the abuses. It also sets out how Her Majesty's Revenue and Customs (HMRC) included an error in its figures which defies belief. The £1.9 billion mistake was in calculations which set the baseline for judging its success in reducing avoidance.

Simply put, by incompetence or by design, HMRC rigged the game, making its targets easier to achieve and presenting an overly glossy picture of its effectiveness.

This led it to mislead parliament, suggesting the department was doing better at cracking down on avoidance than is actually the case.

The Public Accounts Committee wants much more transparency. Parliament has already legislated to help reduce tax loopholes. The committee says HMRC should report on how it is using the new powers to tackle avoidance and demonstrate that it is doing so with urgency.

This would do much to restore the battered credibility of a system which seems to punish relatively minor miscreants, yet remains reluctant or unable to confront large-scale organised abuse of the system.

HMRC needs to be properly staffed for its task. Yet up to 300 jobs are to be lost at the department this year. This will not help it stay ahead of the game.

There are concerns in the report that some organisers of corporate "tax-planning" schemes, to use the legal euphemism, deliberately delayed investigations so time limits for legal action expired. But HMRC and the Government could first change the rules to make such delaying tactics illegal, or arrange exceptions to the time bar. Then, having done so, they can go after the tax avoidance.

For all the vocal concern about abuse of benefits, this behaviour cheats the public in much the same way. Campaigns such as UK Uncut have highlighted a general perception that tax avoidance may not be illegal, but the public feel it is immoral. HMRC must take this problem seriously, and demonstrate that it is doing so.