Not even the Conservatives used to agree with Cameron's anti-tax hike law

UK Prime Minister David Cameron announced Wednesday that, if he is re-elected, the Conservative party will pass a law to ban rises in income tax, National Insurance and VAT over the next parliament within 100 days of getting back into office.

In an election marked by poor policy suggestions from all parties, this one surely just raised the stakes.

Using legislation to ensure that a government enacts its campaign pledges doesn't exactly suggest that the public has much confidence in the party. At least that was the Conservative party's position only five short years ago.

As then-shadow Chancellor George Osborne said of Labour's 2010 Fiscal Responsibility Bill (emphasis added):

Of course we have to debate this vacuous and irrelevant legislation, but why did the Chancellor feel the compelling need to introduce it? Why is he the first Chancellor in history to feel that he needs an Act of Parliament on top of a Budget statement? There can be only two explanations: either he does not trust himself to secure sound public finances, or he knows that the public do not trust him to secure them. Neither is exactly a ringing endorsement; both are a reflection of the catastrophic, disastrous state to which this Government have reduced the finances of this country.

Given the damning indictment of Labour's attempt to use the threat of action by the police where concern for the electorate's reaction should suffice, it seems odd that the Prime Minister has elected to go down this particular rabbit hole.

At the bottom of it he is likely to find a very weird world indeed. One at which the Wonderland central bank's interest rates are already at (or very close to) the zero lower bound, meaning that it doesn't have much room to respond to an economic setback by cutting interest rates, while the Red Queen's government is busy tying its own hands on tax and spending to prevent it from being able to take up the slack.

Taken in combination with the Conservative party's commitment to run a fiscal surplus by 2018-2019, banning tax hikes by law would make the UK more vulnerable to economic setbacks as well as reducing the government's capacity to meet its spending commitments. In effect, Cameron is saying that the government would cede active control of levers that account for some 65% of all tax revenues.

As the BBC's Robert Peston points out, ratings agencies would take a dim view of such unnecessary fiscal handcuffs and could look to review Britain's top sovereign debt rating.

But more fundamentally, this comes down to a very simple point. You might believe that the government will not need to shift tax bands over the course of the next parliament, but that is very different from claiming that it should not be able to do so even if the need arises. And that is what the proposed legislation suggests.

As such it also imposes a huge potential burden on unprotected taxes, such as corporation tax, which could be forced to take the brunt of hikes if the situation did require it. That could well have unintended consequences in terms of sharply reducing the incentives businesses have to stay and invest in Britain.

At its heart, this policy is a huge gamble on that ability of the UK to get through the next five years without encountering any sort of shock. Either it amounts to profound recklessness on Cameron's part or gross deception of the public.