British Prime Minister Rishi Sunak on Sunday hit out at trade unions for causing misery for millions with “particularly cruelly timed” strikes over the Christmas holiday period as the government announced plans to use around 1,200 troops to cover for striking workers to keep key services going.

There is a wave of winter strikes planned over the course of the next few weeks, including railway workers, healthcare workers, and border security staff, who are all demanding better pay and working conditions.

Writing in "The Sun on Sunday", Sunak said the workers have been offered "deals that are fair and affordable" and accused the unions of unleashing a “class war”.

“The unions are causing misery for millions, with transport strikes in particular cruelly timed to hit at Christmas,” writes Sunak.

“Rail workers and border officers have been offered deals that are fair – and affordable to taxpayers. An increasing number of union members want a deal. They are tired of being foot soldiers in [Railway RMT Union chief] Mick Lynch's class war,” he said.

The government has repeatedly warned that giving in to union demands for massive pay rises will kick Britain into an “inflation spiral”, which in turn would hit the poorest the hardest.

"Even [Opposition] Labour have admitted the unions' demands are unaffordable. But they'll still take union money and undermine the interests of the travelling public. Labour back the Grinches that want to steal Christmas for their own political ends. We are doing everything we can to ensure people get the Christmas they deserve,” said Sunak.

"The army is stepping up and we're putting in place other measures to keep services running where possible," he added.

Union chiefs warn the military are not "sufficiently trained" to guard the country's borders or drive ambulances, and that they should not be put in such an "invidious" position when they already have "enough on their plate".

Labour's shadow minister for immigration, Stephen Kinnock, called the Prime Minister's language "incendiary", telling ‘Sky News' that the government is "spoiling for a fight" with the unions.

"I think the government needs to stop all the rhetoric, the empty posturing and sowing the seeds of division and actually now needs to start finding a constructive solution so that we can get people back to work in a way where they feel valued and where they feel that there is a real future for them in those jobs," said Kinnock.

Meanwhile, nurses are threatening to stage a fresh wave of strikes in the new year on an even larger scale if ministers fail to respond with a solution in the 48 hours following next week's walkout.

The 48-hour countdown will begin after the Royal College of Nursing (RCN) stages its second set of historic strikes on Tuesday.