Keir Starmer and Rachel Reeves are still a long way from being ready for government

The opposition has tough questions to answer on its tax and spending plans, writes John Rentoul

Any deviation from Tory plans for tax or spending will have to be accounted for, and made to fit restrictive rules (PA)

George Osborne knows what it is like to be shadow chancellor for a party that is expected to form the government after the next election. He told Andrew Neil on Sunday that the pressure on him suddenly increased – a “blast of incoming fire” – because he had to have answers to questions about how the incoming government would tax and spend.

He said that Rachel Reeves was now in the same position, and there were some big gaps in Labour’s plans. Ed Balls, who was also on the programme, agreed: “That is not a sustainable line that we’ve just heard from Lisa Nandy,” he said. The shadow levelling-up secretary had been asked by Neil how a Labour government could borrow an extra £28bn a year for its climate plan and keep to its target of having debt fall as a share of national income.

Balls said “Labour has got time” and Reeves would come up with a policy, but there was no way that the current holding line – that the climate plan is an exception from the fiscal rules that would otherwise bind a Labour government as tightly as a Conservative one – would last for long.

So far, Labour is helped by the obscurity of the fiscal rules, but the more the conviction takes hold that the party is likely to form the next government, the more journalists such as Neil will ask difficult questions about them.

The next time Reeves gives an interview, she will be asked the same question. I am told that Labour is still committed to the climate plan, and shadow ministers are still briefed to quote the Office for Budget Responsibility, which said that delaying action would mean the costs of reaching net zero would double.

They are also told to say that the party will show at the next election how its Green Prosperity Plan can be delivered within its “strong fiscal rules”. But Reeves is going to come under pressure to explain that now, given that the two things look incompatible.

The problem is made worse for Reeves by Jeremy Hunt’s little-noticed addition to the government’s fiscal rules, which I pointed out the day after the autumn statement. As well as debt falling as a share of GDP, Hunt set a target for the annual deficit to be no more than 3 per cent of GDP. This is the old Maastricht rule, one of the tests for any country wanting to adopt the euro, although it is currently suspended for eurozone members. It is a standard rule for fiscal prudence in normal times and would further constrain a Labour government’s ability to “borrow to invest”, which has been the fashion in recent, low-interest times.

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So far, Reeves hasn’t said anything about the 3 per cent rule, but Labour will have to adopt it. Otherwise the Conservatives will say that she and Keir Starmer intend to let borrowing rip at a time when interest rate payments are already eating into the public finances.

The pattern has been set since 1997. Oppositions have to fight elections taking government plans for tax and spending as their baseline. In 1997, Tony Blair and Gordon Brown accepted Conservative spending plans for the first two years of their government. In 2010, the election was fought over rival plans to reduce annual government borrowing by a lot (Tories) or a sensible amount (Labour and Lib Dems), but all parties accepted the starting point.

Starmer and Reeves will have to do the same. Any deviation from Tory plans for tax or spending will have to be accounted for and made to fit restrictive rules. So far, Labour simply say that the rules will be met, without explaining how. As Balls said, “that is not a sustainable line”, and Reeves will have to come up with a better one soon.