OPINION - The truth about tax no party will tell you

Conventional wisdom dictates that Theresa May made a terrible mistake in calling the 2017 general election. Of course, the result itself – turning a small Conservative majority into a minority – was a political disaster and a personal humiliation for the prime minister. But May had good reason to go to the polls when she did.

First, she was correct in identifying the need for as large a majority as possible in order to get her Brexit legislation through parliament. Second, she was hamstrung by a seemingly unrelated issue: taxation.

Earlier that year, chancellor Philip Hammond had been forced to scrap plans in the Budget to increase national insurance rates for self-employed people. This was because the 2015 Conservative Party manifesto had pledged not to raise national insurance.

That David Cameron and George Osborne – the two key architects of that document – were long gone was besides the point. A manifesto commitment was a manifesto commitment. May came to the conclusion that she required a mandate of her own. The mistake was not calling the election, but in its execution.

I mention this because tax locks – that is, pledges not to raise specific taxes – are nothing new. But they store up problems for the future by constraining the choices made available to the next government. And in the words of Paul Johnson, director of the Institute for Fiscal Studies, when it comes to tax locks, both Labour and the Conservatives have "gone to town".

Johnson accused the two main parties of being complicit in a "conspiracy of silence" on their spending plans, and that consequently, people will be voting in a "knowledge vacuum". But he left his most stinging criticism for Reform UK and the Greens, who he charged with helping to “poison the political debate” by claiming to have radical ideas "which can realistically make a positive difference, when in fact what they propose is wholly unattainable".

This is maybe the six or seventh newsletter or column I've written in the last year that has alluded to the total guff that is Labour/Tory spending plans. The reality is that, four weeks into this election campaign, we don't know what the next government will do. All I can tell you is that Keir Starmer is not going to come into office following the first Labour victory in 19 years and slash spending, as current plans would suggest.

Perhaps it was always like this. The public never knows exactly what it is voting for. For example, the 1979 Conservative manifesto was hardly an orgy of Thatcherite policies. Indeed, according to not wholly reliable narrator Ken Clarke, Thatcher only became a Thatcherite in the late 1980s "when people persuaded her there was something called Thatcherism to which she was the leader." Instead, we vote as we live our lives – in the broad brush, assuming Labour will spend a little more, the Tories a little less.

Ultimately, if voters don't trust politicians, the feeling is mutual. Various opinion polls suggest that the public are prepared to pay higher taxes in order to fund better public services. But, in the sanctity of the polling booth, parties of all stripes suspect subterfuge.

None of this is honest, but to borrow one of my favourite lines from the economist Paul Krugman, politics isn't a morality play. Virtue isn't rewarded and vice punished. Prime ministers and pretenders just go on, making promises and hoping the music doesn't stop on their watch.

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