Christmas getaway journeys were ruined for tens of thousands of people on Thursday after cross-Channel rail services were suspended due to an unexpected strike in France.

The industrial action is affecting Eurostar – which operates passenger services to and from London St Pancras – and Eurotunnel Le Shuttle, which runs vehicle-carrying trains to and from Folkestone.

At least 30 Eurostar trains have been cancelled.

The M20 coastbound carriageway between Junctions 8 and 9 has also been temporarily closed due to suspended Eurotunnel services, Kent Police said.

The “emergency measure” will allow freights bound for the continent to queue on the empty section of motorway to try to minimise disruption to Kent’s wider road network.

A Eurostar spokesperson said: “Due to a last-minute strike by Eurotunnel staff, no Channel Tunnel crossings have taken place since…midday.

“Unfortunately, this means 30 Eurostar trains have been cancelled out of London, Paris or Brussels until the end of the day.

“For passengers due to travel tomorrow, Eurostar will update them directly with any changes to services from 1900UK/2000CET (Central European Time).”

They added: “Customers who have been affected today have received direct communication about their journey and had the option to exchange their tickets free of charge or claim a refund.”

The last two Eurostar trains from London, due to depart from St Pancras International station at 19.01 and 20.01, have been cancelled.

Earlier, several trains were already heading towards the Channel Tunnel when they were forced to return to their starting point.

The Port of Dover also announced a 90-minute wait time for tourists at French border control, as a result of additional volumes of freight and tourists due to the suspension of services at the Channel Tunnel.

News agency Reuters obtained a statement from Getlink, which owns the Channel Tunnel and operates Eurotunnel Le Shuttle services, which said: “Today’s call for strike action by representatives of Eurotunnel’s French site staff unions has resulted in the complete interruption of service and the closure of our terminals in France and the UK.”

The company reportedly added that trade unions had rejected an offer of a bonus worth 1,000 euros (£867) per employee, demanding a payment worth three times as much.

Strong winds were also disrupting the Christmas getaway on Britain’s domestic railway.

Damage to the overhead electric wires between Milton Keynes and Watford meant all lines between those stations were blocked.

This was affecting Avanti West Coast services between London Euston and Scotland.

TransPennine Express urged passengers to avoid travelling to or from Edinburgh all day on Thursday, and to only make journeys to and from Carlisle and Manchester, Liverpool and Preston after 3pm.

The RAC estimated 13.5 million leisure journeys by car would take place across the UK between Friday and Sunday, up 20% on the three days before Christmas Day last year.

Road congestion was likely to peak on Friday – the last working day before Christmas Day – as drivers embarking on leisure trips competed for road space with commuters and business traffic.

Motorists were being advised to travel before 11am or after 6pm if possible to reduce the chance of being stuck in long queues.

Likely traffic hotspots on the M25 identified by transport analysis company Inrix include clockwise between junction 7 (for the M23/Gatwick Airport) and junction 16 (for the M40/Birmingham), and anti-clockwise between junction 17 (Rickmansworth) and junction 12 (for the M3).

Other motorway stretches expected to see long queues included the M1 north from Woburn, Bedfordshire, to Daventry, Northamptonshire, and the M6 south from Wigan, Greater Manchester, to Stafford, Staffordshire.

National Highways said it had removed more than 1,000 miles of roadworks on England’s motorways and major A-roads, meaning 98% of its network would be free of cones over the festive period.

RAC spokeswoman Alice Simpson said: “Strong winds will make many Christmas getaway trips more challenging this week, especially those made in the north of the UK.

“Drivers will need to be on high alert for fallen branches, and even trees, along with other debris as they head to and from motorways and major roads.

“While windy conditions tend not to cause a spike in breakdown volumes, going over debris can lead to more punctures and other, more serious damage to vehicles.”

Network Rail is preparing to launch its festive engineering works, which will cause disruption to journeys.

London Paddington will be closed between Sunday and December 27, meaning no mainline trains will serve Heathrow Airport during that period.

London King’s Cross will also be closed on Christmas Eve.

Outside of the capital, an engineering project near Southampton will cause some disruption to services, as will work to build the new Cambridge South station.

No trains will operate on Christmas Day, while a very limited service will run on Boxing Day.

Meanwhile, millions of people are heading to airports to catch flights to spend Christmas overseas.

Travel trade organisation Abta said the most popular destinations were the Canary Islands, Cyprus, Dubai, southern mainland Spain and Turkey, highlighting the demand for winter sun trips.