If today’s massive “fiscal stimulus” is the Labour Government’s biggest gamble, David Cameron’s decision to oppose it is for him and his party just as crucial. From the moment that Alistair Darling sits down, the Conservative leadership will accuse him of recklessness for which the country will pay later. If they can persuade people they are right, victory at the next election is probably assured.

The spectacle of their Shadow Chancellor standing up to criticise a swath of tax cuts, including a straight chop off the VAT rate, will inevitably cause misgivings among some in his party trying to restore its reputation for tax-cutting. Mr Darling’s insistence on spelling out today how the “giveaway” will be paid for helps to make the Tory case. Everyone from Gordon Brown down is admitting that there will have to be tax rises later.

In another way it is less than helpful. It makes it harder for the Tory charge of a hidden cuts agenda to stick if the figures are out in the open, and it also tells people that, whoever is in charge after the election, taxes will have to rise and spending will have to be cut.

Mr Cameron and George Osborne accept fully that they have a difficult path to tread. Mr Cameron tried yesterday to keep open the possibility of not voting against tax reductions. But he said he was sceptical about the expected VAT cut – tentatively supported by Kenneth Clarke in The Times on Saturday – which he said would add £12 billion more to record borrowing with no guarantee of extra high street activity.

As Labour MPs wave their order papers in triumph at about 4.15pm today, however, Mr Osborne knows that he will be cast as a latterday Scrooge as he speaks out against a package designed to put more money into the economy and people’s pockets, that has been backed by business organisations and which will be followed by other governments. It will be an occasion that underlines the power of government to do things, and the impotence of opposition.

It is not, however, a position that the Tory leadership has come to by accident. They have consulted a quartet of former chancellors, former Treasury mandarins and a range of economic experts, as Mr Cameron disclosed yesterday. It has led them to the conclusion that the tax-cut-and-spending package today is irresponsible and will be shown by events to have been so.

They believe that people will be deterred from spending today’s tax cuts by the knowledge that tax rises will come later on, and they maintain that today’s apparent munificence could curb the likelihood of further significant cuts in interest rates. They believe that as the recession bites, Mr Brown’s recent polling bounce will be punctured, swiftly killing talk of an early election.

They say that the public will be shocked when Mr Darling reveals the true level of government debt. The Government is going on a borrowing “binge” but one that will result in much higher taxes.

The Tories will relaunch their Labour “tax bombshell” campaign today, which was credited with playing a big part in their surprise 1992 election victory.

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