During his round of BBC interviews, Sir Keir was also pressed on farmers’ unhappiness about changes to inheritance tax, the rise in energy bills and the continuing increase in the number of migrants arriving from across the English Channel.

Asked why he thought he would succeed in reducing the number of small boat crossings when previous prime ministers had failed to do so, he said he was focusing on “working with other countries on law enforcement to take down the gangs that are running this trade”.

A coalition of French mayors has called for an end to a deal that allows UK immigration checks to be carried out before crossing the Channel, but Sir Keir told Radio Kent he was “determined” they would continue.

He said he would be “taking this up with the French authorities”.

Earlier this week, thousands of farmers and supporters gathered in central London to protest against Budget measures, including the imposition of inheritance tax on farms worth more than £1m and speeding up the phasing out of EU-era subsidies in favour of nature-friendly farming payments.

On agricultural inheritance tax. the prime minister again said the vast majority of farms would be “completely unaffected”.

When it was put to him on Radio Lincolnshire that some family farms would be put out of business by having to pay inheritance tax, he replied that in a typical case, where a farm was first passed to a spouse and later to a son or daughter, the threshold before the tax was payable would be £3m.

“There aren’t many farms year on year that are sold in excess of that amount, and therefore that threshold is high,” he said.

Sir Keir denied claims on Radio Bristol that he was on the side of farmers or small business owners, or “for keeping millions of pensioners warm”.

Asked who he was for, he said: “We’re for working people who need to be better off, who’ve really struggled over recent years.