Chancellor Rachel Reeves has said she will make “necessary choices” in the Budget after the “world has thrown more challenges our way”.

Her Downing Street speech did not rule out a U-turn on Labour’s general election manifesto pledge not to hike income tax, VAT or National Insurance.

When journalists explicitly asked if the government was set to break that pledge she did not answer directly but said she was “setting the context for the Budget”.

Ahead of the speech, shadow chancellor Sir Mel Stride dubbed it an “emergency press conference”, adding “higher taxes are on the way” and called for Reeves to be sacked if she “breaks her promises yet again”.

If there was any doubt about tax rises before this speech, there isn’t now.

Yet Reeves repeatedly refused to get into the specifics of which taxes might go up.

Instead she began the work of explaining why a year after delivering a tax-raising Budget and vowing not to come back for more, she is in fact coming back for more.

The chancellor said she would do what is necessary, not what is popular.

The reasons she gave were poor productivity, for which she blamed Conservative government policy including Brexit, austerity and short-sighted decisions to cut infrastructure spending, persistently high global inflation and the uncertainty unleashed by Donald Trump’s tariffs.

In short, Reeves’ argument is that the failings of others are being visited upon this government, and that it falls to her to confront decisions her predecessors ducked.

She pledged to come up with a “Budget for growth with fairness at its heart” aimed at bringing down NHS waiting lists, the national debt and the cost of living.

“It is important that people understand the circumstances we are facing, the principles guiding my choices – and why I believe they will be the right choices for the country,” she said.

There are some in government who want this to be a one-and-done Budget, in that they do not want to come back again and again every year, eking out a bit more money in tax to meet the requirements of the independent forecast.

That is seen as an argument for raising billions of pounds through increasing at least one of the income tax rates.

However, no chancellor has increased the basic rate in 50 years and it would be a big risk politically, especially with public trust in politics in general, and Prime Minister Sir Keir Starmer in particular, so low.

There is also the question of whether the prime minister and chancellor could land the argument that none of this was foreseeable before last year’s Budget.

The message from Reeves echoed comments made by Sir Keir to a group of Labour MPs on Monday night.

He told those gathered that the Budget would be “a Labour Budget built on Labour values” and that the government would “make the tough but fair decisions to renew our country and build it for the long term”.

It comes as the Resolution Foundation, which has close links to Labour and was previously run by Treasury minister Torsten Bell, said avoiding changes to VAT, NI or income tax “would do more harm than good”.

Hiking income tax would be the “best option” for raising cash, it said, but suggested it should be offset by a 2p cut to employee national insurance, which would “raise £6 billion overall while protecting most workers from this tax rise”.

Extending the freeze in personal tax thresholds for two more years beyond April 2028 would also raise £7.5 billion, its pre-Budget analysis suggested.

The government’s official forecaster, the Office for Budget Responsibility (OBR), is widely expected to downgrade its productivity forecasts for the UK at the end of the month. That could add as much as £20bn to the amount the chancellor will need to find if she is to meet her self-imposed “non-negotiable” rules for government finances.

The two main rules are:

• Not to borrow to fund day-to-day public spending by the end of this parliament

• To get government debt falling as a share of national income by the end of this parliament

The Treasury declined to comment on “speculation” ahead of the OBR’s final forecast, which will be published on 26 November alongside the Budget.

However, the chancellor confirmed last week that both tax rises and spending cuts are options as she aims to give herself “sufficient headroom” against future economic shocks.

Reeves said in her speech on Tuesday that her commitment to her fiscal rules was “iron-clad”.

The Resolution Foundation urged the chancellor to use the Budget to give herself more fiscal headroom, meaning how much leeway she has to increase spending or cut taxes without being forced to break her own rules.

After the last Budget, Reeves had £9.9bn of headroom – but the think tank said subsequent policy U-turns and changes in the economic outlook have turned that into a £4bn black hole.

The group said Reeves should double the level of headroom to £20bn in order to “send a clear message to markets that she is serious about fixing the public finances, which in turn should reduce medium-term borrowing costs and make future fiscal events less fraught”.

Last month, the Institute for Fiscal Studies (IFS) said there was a “strong case” to increase fiscal headroom.

The think tank said the lack of a bigger buffer created instability, and could leave the chancellor “limping from one forecast to the next”.