British people will have to endure even worse economic and social ­pressures in the months to come as the Labour government takes “unpopular decisions” to rebuild the country from “rubble and ruin” left by the Tories, Keir Starmer will warn this week.

With the prime minister under mounting pressure from within his own party to help people struggling with rising fuel payments and millions of families in poverty, Starmer will strike a defiant note against those demanding U-turns from his ministers, saying “tough choices” will have to be made before any recovery is possible.

Starmer’s speech on Tuesday is being billed by Downing Street as “a direct message to the working people across Britain”.

He will say that the “rot” left by the Conservatives is so deep and so much worse than he had imagined that improvement “won’t happen overnight”.

The prime minister will make the extraordinary claim that those who took part in recent riots were doing so because they knew society had been left broken and that there were not enough prison places.

“Not having enough prison spaces is about as fundamental a failure as you can get,”he will say.

“Those people throwing rocks, torching cars, making threats – they didn’t just know the system was broken. They were betting on it. They were gaming it. They saw the cracks in our society after 14 years of populism and failure – and they exploited them. That’s what we have inherited.”

Starmer will deliver the tough messages in a speech before the return of MPs to Westminster on 2 September, setting the stage for a serious of difficult decisions on tax and spending this autumn.

He will say his government has inherited “not just an economic black hole but a societal black hole”, adding that “this is why we have to take action and do things differently. Part of that is being honest with people about the choices we face. And how tough this will be.”

He will say: “Frankly, things will get worse before we get better.”

Since Labour’s landslide victory in the 4 July general election, Starmer and the chancellor, Rachel Reeves, have been at pains to blame the Tories for leaving them with a terrible inheritance and no room for financial manoeuvre.

But with MPs returning from their summer breaks and the party conference season approaching, Starmer is facing growing demands from many of his own MPs and the unions to deliver more help for those facing economic struggles, rather than additional austerity.

A string of motions has been tabled to the TUC conference early next month calling for emergency wealth taxes to fund a massive ­boost to public investment, the end of the two-child cap on benefits and the scrapping of the recently announced restrictions on winter fuel payments.

Before her first budget as chancellor on 30 October, Reeves is facing calls to perform a U-turn, and the threat of rebellion, over her recent announcement to limit the winter fuel payment to only the poorest pensioners.

The issue flared into an incendiary row on Friday after the energy ­regulator announced, as had been widely predicted for months, that gas and electricity prices would be rising by 10% this winter.

On Saturday, party grandee Harriet Harman gently hinted that the party might have to shift its position and adopt “a different cut-off point” for winter fuel payments, adding in an interview with Times Radio that such discussions might be under way.

The financial expert Martin Lewis, meanwhile, has suggested that the benefit should be widened to include all pensioners in council tax bands A to D, taking in far more households, and easing the pressures on the many of the poorest.

Many Labour MPs are furious that a policy to restrict winter fuel payments was announced shortly before the pricing decision by the energy regulator, which had been known about and predicted for many months.

The Labour MP for York Central, Rachael Maskell, said that changes to the policy were needed if Labour were to show that it really cared about the poorest and most vulnerable.

She said: “With winter on its way, when parliament returns, MPs will need a package of support to reassure our constituents that Labour will help them through this winter with their energy costs.

“Many will struggle if the Social Fund Winter Fuel Payment Regulations 2024 pass in September without changes being made or being withdrawn altogether.

“While longer-term reforms are needed, and work on reducing energy bills has started through Ed Miliband’s energy sprint to renewables and retrofit programmes, the challenge facing older people right now are the winter months ahead.”

Another Labour MP said the worry was that “old people will get ill and will die”, adding: “Old people won’t put on the heating – they don’t like getting into debt. It is not what they do. We have to move on this.”

The prime minister will argue that sacrifices now are the only way to get long-term benefits for the whole of society: “I won’t shy away from making unpopular decisions now if it’s the right thing for the country in the long term. That’s what a government of service means.

“This shouldn’t be a country where people have to fear walking down the street, or watch cars and buildings being set on fire. This shouldn’t be a country where the prime minister can’t guarantee prison spaces. But it also shouldn’t be a country where people are paying thousands more on their mortgage or waiting months for hospital appointments they desperately need.

“So, when I talk about the inheritance the last government left us – the £22bn black hole in our finances – this isn’t about lines on a graph, this is about people’s lives.

“And the Tories are still not being honest about it. They haven’t recognised what they’ve cost the country and they haven’t apologised for what they’ve cost you.

“But I promise this: you will be at the heart of our government, in the forefront of our minds and at the centre of everything we do. That this government is for you, back in your service.”