The UK business secretary, Jonathan Reynolds, has said the government has “no choice” over cutting the winter fuel allowance, and urged Labour MPs to back the plan ahead of a Commons vote on the issue.

Acknowledging that it was a difficult decision that reflected the dire state of public finances, he urged colleagues to “recognise and support” the policy in Tuesday’s vote.

Keir Starmer, addressing the Trades Union Congress in Brighton, was unapologetic over some of his controversial choices. “I make no apologies for any of the decisions we’ve taken to begin the work of change,” he told union delegates.

However, the prime minister appeared to acknowledge concern over his downbeat rhetoric since the general election. “No one in this room wants to hear such a gloomy forecast and I get that. I don’t want to be saying it either. It’s not how any government would want to begin its work,” he said.

Starmer received a warm, although muted, response from the hall, but his speech prompted warnings from union leaders over cuts to the winter fuel payment and plans for public services.

Fran Heathcote, the general secretary of the PCS union, said: “We’ve had enough of being told about ‘tough decisions’. The real tough decisions are forced upon our members every day trying to make ends meet.

“Thousands of the government’s own workers earn just above the minimum wage and are having to rely on food banks. There will not be a stronger economy without boosting the incomes of working people. You cannot solve the problems caused by austerity with more austerity.”

Jo Grady, the general secretary of the University and College Union, said: “Starmer is right to point out the mess the Conservatives left us in, but we now need solutions. Pensioners don’t need to freeze this winter, nor should public institutions be left to crumble.

“Labour needs to move on from blaming the Tories and start rebuilding Britain. This means higher taxes on the rich and massive public investment.”

Reynolds, speaking on Times Radio, said: “Fixing the foundations of the country isn’t just about difficult things like this, which are decisions that ideally you wouldn’t have to make. It’s about how you get to a better future.”

On Sky News, the minister told MPs: “We’ve got to be the team that fixes this country. Don’t rely on your colleagues to make the difficult decisions that are necessary.”

Reynolds insisted the government had no choice over cutting winter fuel allowance, pointing to commitments such as compensation for post office operators and money for the steel industry, while defending the decision to spend on a 5-6% pay increase for public sector workers.

Asked why the policy had not been in the Labour election manifesto, he said the party “did not know the situation we would inherit”, and now had no choice.

He also said it was not fair to suggest that Rachel Reeves was behaving like “the Grinch” over the cut, an accusation levelled at the chancellor by the RMT general secretary, Mick Lynch, at the TUC Congress on Monday.

“I don’t think that that is fair in any way,” Reynolds told LBC. “What we have been able to do is first of all be serious about decisions that the previous government has sat on … it’s nothing like the kind of austerity that we saw under George Osborne.

“It is a recognition that where the previous government has made commitments that it can’t honour, you’ve got to be responsible within there.”

Reynolds rejected the suggestion that pensioners could die of cold this winter as a result of the government’s policy.

Asked whether he and the government accepted this was a possibility, he told BBC Radio 4’s Today programme: “No. We are making sure that we can reassure people by saying the state pension is higher than last winter and energy bills are lower than last winter.”

He said pensioners would be better off this winter because the state pension was rising, bills were falling, the warm homes discount was available, the government was committed to the pension triple lock, and he urged those who had not yet claimed pension credit to do so.