REVEALED: Keir Starmer's right-hand man warned PM that Nigel Farage holds four key cards to sink Labour

The 48-year-old Irishman pointed out that being soft on net zero, immigration, delivering change and by being associated with a failed establishment tends to embolden the so-called populist right.

He also outlined a blueprint for tackling Reform UK, including levelling with the public, going on the offensive, telling a coherent story and refusing to duck the key issues.

In extracts of the memo, which was penned by McSweeney last year and acquired by The Spectator this week, the Prime Minister was warned: "Without an approach [to net zero] led by political strategy, the populist right can position itself as being on the side of working people, against a government captured by the moral imperative to decarbonise.

"A small group of voters, who live largely in safe Labour seats, feel climate change is a key issue, and an equally small group, on the right of the Tory coalition, are fully-fledged deniers.

"Most, and particularly swing voters, take a nuanced view.

"They think climate change is real, but working people should not be forced to pay to solve the problem, and that the Government should focus on issues that more immediately affect them.

On migration, McSweeney added: "We must be tough from the start.

"The first things we do on migration must be about getting control over our borders, smashing the gangs, and tackling small boats.

"We must earn the trust to address more fundamental challenges: Home Office reform, or more boldly, reframing legal migration as a matter of industrial strategy by moving legal migration out of the Home Office and into the Department for Business and Trade (DBT).

"What we say and do must constantly underscore the argument that the Tories lost control of our borders, and we are taking it back."

In a direct swipe at Farage, the Irishman later wrote: "Attacking your opponents matters as much in government as in an election campaign or opposition.

"Done well, it enables you to define – and toxify – your opponents before they define themselves.

"After the election, the Conservatives will find themselves in a painful and prolonged debate, in which its relationship with Farage, probably as an MP, will become existential.

"While they are distracted, Labour quickly cement their culpability for Britain’s ills in voters’ minds. This is what the Conservatives did in the summer of 2010.

"While Labour was debating its future, the Conservatives ruthlessly and relentlessly pinned the blame for the financial crisis on Labour.

"The starting point must be to endorse the depth of the disillusionment, even rage, many feel. Voters aren’t wrong to believe that politics has stopped serving working people.

"It has. Worse, it has started to serve itself. In the most egregious cases, politicians have used their office to enrich themselves and their friends.

"Voters have been let down by their leaders. The system has been rigged against working people.

"The people who did that are the Conservatives. In Government, we must continue to be streetfighters in communication and campaigning, putting our opponents on the defensive.

However, The Spectator suggested that McSweeney's thinking has changed somewhat since he penned the dossier before the 2024 General Election.

Despite speculation that McSweeney is now following a different path, No10 insiders were said to have discussed the memo just last week.

It has been a turbulent time for the Prime Minister, with an enormous climbdown on cutting benefits appearing to smash away at his authority.

Starmer will hope his second year is somewhat smoother than his first, but it is hard to imagine that the spectre of Farage is going to go anywhere any time soon.