Interior minister Suella Braverman warned the public against flying over Christmas, after passport control officers voted to walk out.

"If they go ahead with those strikes there will be undeniable, serious disruption caused to many thousands of people who have holiday plans," Braverman told reporters.

The Border Force agency is training 2,000 soldiers to back up its personnel, officials said.

The Ministry of Defence is also in talks with the National Health Service, Downing Street said, after ambulance drivers voted to join nurses in striking this month.

The passport control staff and ambulance drivers have joined many sectors who have opted for strike action this year as decades-high inflation erodes the value of earnings.

- 'Rolling strikes' -

"These sorts of rolling strikes will cause disruption for everyone," Prime Minister Rishi Sunak's spokesman told reporters, reiterating the government's opposition to inflation-busting pay deals.

"And that does also include our military personnel who will be required, unfortunately, to have to step in and backfill some of these vital roles that we need to help keep the country moving."

Sunak on Wednesday hinted that ministers were preparing new legislation to outlaw strikes in critical sectors.

Currently, only Britain's police, military and prison guards are barred by law from striking.

"What we're looking at is, are there other areas that we should include in that?" Education Secretary Gillian Keegan told BBC radio Thursday.

"Health would be one to look at and other areas of critical infrastructure," she added.

The government has yet to look at banning strikes by teachers, who have gone on strike in Scotland and are being balloted in England and Wales, she said.

- 'Christmas chaos' -

Ahead of a new wave of train strikes beginning next week, rail union leaders said the government had blocked a deal to end their long-running dispute over pay and other conditions.

"Rail workers and the industry have been put in an impossible position by the Tory government," Frank Ward, interim general secretary at transport union TSSA, said Thursday.

"Christmas chaos and disruption across our railways are now unfortunately guaranteed, and come gift wrapped from Rishi Sunak and his anti-worker Conservative government's agenda."

The government is pushing through a law to require a minimum service on the railways and has refused to rule out expanding that bill to encompass other public sectors.

But Britain faces a winter of discontent as strikes multiply in the face of spiralling consumer prices. Many travellers will struggle to get home for Christmas as transport staff walk out.

Airports, buses, railways and roads face potential gridlock as a result of strikes, which will also hit Eurostar services.

And Britons face chronic delays to Christmas cards and parcels as walkouts continue to blight postal operator Royal Mail.

Nurses will also walk out next week for the first time in their union's 106-year history.

- Cost-of-living crisis -

British inflation stands above 11 percent, the highest level in more than 40 years.

"I don't think those going on strike want strikes and disruption," Keir Starmer, the leader of Britain's main opposition Labour party, said Thursday.

"They are facing a very real cost-of-living crisis, they are struggling to pay their bills," he told business leaders.

The Financial Times estimates that more than one million working days will be lost to industrial action in December.

Analysts however talked down the overall economic impact.

"While the strikes feel quite widespread, in practice only a small share of the workforce will be on strike at the same time," noted Paul Dales at research consultancy Capital Economics.

He conceded however that "any hit" to economic activity "is not helpful when the economy is probably already in recession".

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ROYAL MAIL