After a campaign previously monotonously devoted to their "long-term economic plan", the Tories have shifted into populist mode. Yesterday saw them promise to freeze rail fares in real-terms for the duration of the next parliament. Today they have pledged to spend £8bn a year more on the NHS by 2020 (matching the sum requested by health chief executive Simon Stevens). In a rare article in the Guardian (reminiscent of the Conservatives' "modernisation" phase), George Osborne writes: "I can confirm that in the Conservative manifesto next week we will commit to a minimum real-terms increase in NHS funding of £8bn in the next five years. That is a minimum of £8bn over and above the £2bn down payment that I announced in the autumn statement last year. We’ve funded the NHS through the last five years; today we commit to fund it for the next five years." This exceeds the £2.5bn promised by Labour, which the party would raise through a mansion tax on properties worth more than £2m, a windfall levy on tobacco companies and a crackdown on hedge fund tax loopholes.

What Osborne's piece doesn't include is any explanation of how the Tories will meet this pledge while simultaneously eliminating the £90bn deficit and avoiding any further tax rises. The same was true in the case of the rail fares offer and the promise at last year's Conservative conference to cut taxes by £7.2bn (through an increase in the personal allowance to £12,500 and a rise in the 40p rate threshold to £50,000). To this already foreboding bill will be added a commitment to raise the inheritance tax threshold to £1m when the party's manifesto is launched on Tuesday.

One might expect the Tories, who have long prided themselves on their reputation for fiscal responsibility, to avoid making such reckless and unfunded pledges. But the reverse is the case. Indeed, it is precisely because polls show that they are trusted to manage the public finances that they believe they can get away with such promises. To do otherwise, they believe, would be to waste one of their most precious political assets. Unlike Labour, forced to cost every spending commitment in a bid to combat its profligate reputation, they can play fast and loose. When asked where the money will come from, their reply can be distillled as "just trust us". As Osborne writes in his article: "We can make this commitment because we’ve got the track record and a plan to grow our economy. New figures, confirmed by the Treasury, show that in the five years from 2010-11 to 2015-16 we are set to deliver a real-terms increase of £7.3bn. And we have done that at the same time as halving the deficit as a share of GDP and cutting income tax for 26 million people. In the next parliament we will continue with the same balanced approach."

What he doesn't mention is that in the last parliament he raised VAT to 20 per cent (having previously said he "no plans" to do so) and postponed his plan to eliminate the structural deficit by three years. Osborne writes as if it was always his intention to halve government borrowing. In fact, it was precisely this pledge that he denounced as "woefully adequate" when made by Labour's Alistair Darling. With a "track record" like this, why should Osborne be trusted to stick to his plans this time? The Tories' wager is that voters will give them the benefit of the doubt. But by spraying around spending commitments like Swedish socialists they risk muddying their message. If there is so much spare money around, why do we need to give the axe men another term in government? That is certainly what Labour hopes the public will conclude. But it knows it cannot discount the possibility that the Tories' economic lead (which exceeds 20 points in some polls) is sufficiently robust for them to emerge with credibility in tact. Either way, we don't have long to wait to find out whether Osborne's great gamble pays off.