Opposition parties and financial institutions are actively preparing for Andy Burnham to call an early election on the back of a “boring Budget” this week, despite public denials by the prime minister.

A source close to Kemi Badenoch told that an Ipsos poll out this weekend, which suggests Labour would win a majority of more than 130, has added to their expectation of an election, possibly in May or even earlier.

One Tory source told : “Wednesday’s Budget is the end of the phoney war and when things get serious.

“What’s in the Budget will dictate whether we get an early election or not but, if Burnham gets a few more polls like that, then we are looking at December or May next year maybe autumn next year at the latest.”

A briefing by the London arm of the major Dutch bank ING confirmed that it too is preparing for an early election, and has been told by other City sources that banks and financial services in the UK also anticipate Mr Burnham will go to the country early.

It comes as John Healey is putting the final touches to his first Budget as chancellor on Wednesday, with expectations that he will keep changes to a minimum.

The chancellor is expected to hit banks with a levy increasing the tax on their profits from 3 per cent to as much as 8 per cent. But Mr Healey is understood to have turned down demands from cabinet colleagues for a hike in capital gains tax while he and Mr Burnham have insisted they will stick to Sir Keir Starmer’s election manifesto promise not to raise income tax, VAT or employee national insurance contributions.

There is expected to be more help for energy bills on low income households and measures to bring down fuel duty while the government is expected to put money into Mr Burnham’s plans to end rough sleeping.

The chancellor also appears to be on course for a showdown with the trade unions, some of Labour’s biggest financial backers, by not fully funding public sector pay rises and forcing departments to find the money from within their own budgets as he tries to keep a handle on the nation’s finances.

With Labour hitting its highest point in a poll since the election with 32 per cent from Ipsos – eight points ahead of the Tories and 12 points above a Reform UK on the slide – Ms Badenoch’s inner circle believes an early election is “highly likely”.

They and other opposition parties are putting candidates in place for an early election in target seats, understands.

There are also concerns that the Treasury may attempt to massage the figures in the Budget to conceal the level of the UK’s future debt in a bid to prepare the way for an early election.

The Tories have already raised questions about whether the chancellor will use the Public Sector Net Financial Liabilities (PSNFL) measurement, which is £365bn lower than Public Sector Net Debt (PSND), because it includes theoretical government assets, such as the student loans book.

This would help pave the way for early election pledges, because reduced debt would give Labour more room to make spending priomises.

Shadow chancellor Andrew Griffith said: "The Conservatives will be going through the Budget with a fine-toothed comb to make sure the facts see the light of day."

Meanwhile, ING bank along with others, is expecting “a boring budget, steady as she goes”. ING economist James Smith told a pre-Budget briefing in London that an early election is “under priced”.

He said: “Everything in UK politics at the moment seems to point in that direction. Burnham said back in August that this is a 10-year project. Currently, it's a three-year project.

“Frankly, a lot of these bold ambitions [from Burnham] are the sort of things you do on day one of a five-year term. So people are finding it very difficult to square that whole agenda with frankly quite a boring budget.

“These policies we're hearing about – bus fares and the VAT off energy bills – are eye-catching stuff that don't really cost a lot of money. It's the sort of thing you do if you're going to do an early election.”

But he said the biggest factor was the upcoming spending review, which has already been delayed until next autumn.

“It's the sort of thing you do after an election. I think that’s why there's growing talk about whether you get an election next spring or summer ahead of that.”

He also noted that the promise to review Brexit and consider rejoining the EU makes an early election more likely.

However, he warned: “I think markets probably wouldn't like an early election because I think there's a growing recognition that the UK actually looks quite good on fiscal policy. An early election will certainly be a catalyst for markets to think: ‘Well, how do these big pledges get funded, is it going to be loose of fiscal rules?’”

His view was largely agreed with by Robert Salter, director at tax and accounting firm Blick Rothenberg.

He said: “One of the challenges facing the government from a fiscal policy is the commitment in the Labour Party’s last election manifesto not to raise income taxes, NICs (national insurance contributions) or VAT during this Parliament. In this regard, it is worth remembering that income tax, NICs and VAT are the ‘big three’ taxes from a government tax receipts perspective and hence it is easy to see that the commitment in this area – even if not legally binding – restricts the freedom of the prime minister and chancellor from a tax policy perspective.”

Polling experts remain sceptical about an early election but also warned that the strategy of a “steady-as-she-goes” Budget could also backfire.

Professor Sir John Curtice said: “The risk will be that the government still seems unable to point to better times economically. We are not in early election territory yet.”

Lord Robert Hayward added: “A steady-as-she-goes Budget will simply be interpreted as taxes later. An early election will be too much of a risk because Labour would probably lose its majority.”