Starmer's future was thrown into doubt after his Labour Party suffered heavy losses in local elections last week and a former minister threatened to seek MPs' backing for a leadership contest if he fails to offer radical change.
More than 30 of Starmer's MPs have called for him to quit or to set out a timetable for his departure after the local election defeats, the worst for a governing party in more than three decades.
In his latest government reset, Starmer will say on Monday that "incremental change won't cut it" and the scale of reforms needed to revive the economy, rebuild Britain's military, and boost energy security are bigger than he had realised, according to extracts of the speech released by his office.
Although no new policies were announced in the extracts, Starmer will say his government "will be defined by rebuilding our relationship and by putting Britain at the heart of Europe", almost a decade after Britain voted to leave the European Union.
A pledge to deepen ties with Europe would be popular among Labour MPs and many younger voters, with polls showing that about 60 per cent of Britons now believe leaving the EU was a mistake.
However, efforts to rebuild relations would raise difficult questions, including whether to allow more immigration from Europe in return for better access to European Union markets, and are likely to face opposition from right-wing Eurosceptic parties and some British media outlets.
Starmer won one of the largest parliamentary majorities in modern British history in 2024 with promises to expand the economy, lower illegal immigration, and cut waiting lists in the National Health Service.
However, progress has been hampered by policy U-turns, perceptions among some in his party that he is unwilling to take difficult decisions, and a series of political scandals, contributing to some of the lowest approval ratings of any British prime minister.
Acknowledging that his government had sometimes failed to deliver the change that voters wanted, Starmer will say "people need hope" and that he is ready to "face up to the big challenges" Britain faces.
The pressure on Starmer increased after his former deputy prime minister, Angela Rayner, warned on Sunday in a rare intervention that the Labour Party may be facing its "last chance" to change direction.
Another Labour MP, Catherine West, a little-known Australian-born former junior minister, has called on the Cabinet to oust the prime minister.
She warned that, if it fails to do so and she is unhappy with the contents of the prime minister's speech, she would attempt to trigger a leadership contest herself.
But the Labour Party has never removed one of its prime ministers in its more than 125-year history.
Under the party rules, it would take 20 per cent of the parliamentary party, or 81 MPs, to announce they were backing a single candidate to trigger a leadership challenge.
