So far during this election campaign the demand for candour on the subject of public spending cuts has not been matched by a similar demand for openness and honesty on the need for tax rises. This, despite figures from the Office for National Statistics suggesting that collapsing tax revenues, caused by the economic slowdown and rising unemployment, have played a bigger role in our £167bn Budget deficit than spending increases. The inconvenient truth is that, without tax rises, we will never be able to close the fiscal gap.

But dishonesty prevails among the political class. The three main parties may have been wise not to make a "Read my lips: no new taxes" pledge in their manifestos, but no party leader has yet admitted to the voters, publicly and unequivocally, the extent to which taxes will have to rise in the next parliament. Instead, the parties opt for tactical vagueness. None of the three parties has ruled out a VAT rise in the next parliament. VAT is a regressive tax that hits low-earning households much harder than those on higher incomes.

Labour has, however, ruled out a rise in income tax rates, as it did in the past three elections, despite the irony that when this government broke its 2005 pledge by introducing a new 50p top rate on all earnings of more than £150,000, it proved to be popular with the public. Instead, Labour once more promises a rise in National Insurance. This is a dishonest tax, and is a form of income tax by any other name. For whatever reason - timidity, paranoia, caution - Labour remains afraid to make the case for progressive taxation, at a time when it should be willing to consider merging income tax and National Insurance, and then hypothecating how much of direct taxation is spent on, say, the health service.

The Tories, on the other hand, seem to have returned to their Thatcherite, tax-cutting roots. The party has abandoned fiscal rectitude in this campaign and, in the words of Gordon Brown, has been "spraying around" promises of tax cuts - from the NI reversal to the inheritance-tax cut to the marriage-tax break. One analysis on newstatesman.com suggests that David Cameron is offering more tax cuts in 2010 than his predecessor Michael Howard did in 2005. In fact, while Howard promised only a modest £4bn in tax cuts at the 2005 election, Cameron's tax-cut pledges add up to roughly £18bn. Meanwhile, the Institute for Fiscal Studies (IFS) has concluded that the Tories "would likely need to announce further tax raising measures to get the job done".

But what do we hear from the leading Tories? William Hague says: "We are not looking for tax rises." Kenneth Clarke says the party's approach to business will be based on "low taxes".

There is, too, the Liberal Democrats' pledge to raise the income-tax threshold to £10,000, which many have hailed as a bold and clever move. But, as Nick Clegg conceded during an interview with the BBC's Jeremy Paxman, only £1.5bn of the £17bn cost of the policy would go on taking the lowest earners out of tax. The Lib Dems' deficit reduction is premised on spending cuts alone. The Tories' deficit-reduction plan is also based largely on spending cuts rather than tax rises, by a ratio of 4:1. So too is Labour's, but its ratio is closer to 2:1.

Is any of this credible? "Bear in mind that the ratio of discretionary spending cuts to tax increases in the last big fiscal tightening undertaken by a Conservative government, in the early 1990s, looks to us to have been around 1:1," says the IFS.

So, if history is a guide, as much of the heavy lifting of Britain's fiscal retrenchment will be done by tax rises as it is by spending cuts. When will the party leaders deign to speak the truth to the rest of us?