Eurostar has launched an immediate review into train breakdowns over the weekend which have stranded and delayed tens of thousands of passengers.

Meanwhile trains modified overnight are being tested on Monday, after services were suspended for a third day.

More than 55,000 travellers saw their journeys cancelled after six trains broke down, in what Eurostar said was unprecedented winter weather in France.

The company hopes to announce on Monday evening when services will resume.

But it has warned it will take time to clear the backlog of stranded passengers.

Thousands and thousands of families are having their Christmas ruined this year Transport Minister Sadiq Khan

The review follows the cancellation of services and the trapping of 2,000 passengers on six trains in the Channel Tunnel on Friday and Saturday.

Many passengers spoke of their “nightmare” experiences of hours stuck in the tunnel with little food and water, and an apparently disorganised and unfeeling response from the authorities.

Eurostar said the review would be an independent inquiry led by Christopher Garnett, a former commercial director of Eurotunnel and chief executive of rail company GNER, and Claude Gressier, who is inspector general of bridges and roads in France.

Transport Minister Sadiq Khan said he had asked for the review to report not to the Eurostar board but to him and to shareholders. He said he would be speaking to his French and Belgian counterparts about the issue.

“Thousands and thousands of families are having their Christmas ruined this year,” he said.

A statement on the company’s website said it “sincerely regretted” having to halt services for a third day.

Travellers who had bookings for Saturday, Sunday or Monday will be able to claim “reasonable out-of-pocket expenses” for hotel, transport and meal costs.

EUROSTAR ADVICE If your journey is not essential, do not travel A full refund will be offered to those whose journeys have been affected Passengers whose journeys were severely disrupted on Friday or Saturday will also be given £150 compensation, out-of-pocket expenses, and a free return ticket Those who had bookings for Saturday, Sunday or Monday can claim “reasonable” out-of-pocket expenses such as hotel, transport and meal costs All updates will be posted on the Eurostar website and given out to news outlets Are you a Eurostar passenger?

Eurostar said it believed it had identified the problem, and had modified its trains to try to stop water getting into the electrical systems.

It said snow shields used to protect the electrics had worked for the 15 years it has been running services through the tunnel.

But Eurostar’s commercial director Nick Mercer told BBC News that “acute” conditions in northern France had taken the operator by surprise. More snow is forecast for the area on Monday.

Eurostar has warned it will be not able to carry all of the passengers due to travel over the next few days as well as clearing the backlog.

It is advising people to postpone their trips unless absolutely necessary.

The company plans to make an announcement on progress at 1800 GMT on Monday.

Apologising on behalf of Eurostar, Mr Mercer said the company was taking the situation “very seriously”.

“It is very clear from some of the reports that passengers on those trains, their experiences really were very very poor.”

He said procedures were followed when the trains broke down.

“Safety is our number one priority. Everybody in the Channel Tunnel was evacuated safely.

“But obviously customers were put to huge discomfort in the length of time it took to take people off the trains,” he added.

Passenger compensation

On Sunday Eurostar transported 500 of the most “vulnerable” waiting passengers from the UK to France and Belgium by train, ferry and coach.

Meanwhile travellers from Britain were still stranded in mainland Europe on Monday.

Lauren Copping, from Hoddesdon, Hertfordshire, said her three-year-old son Joshua was stranded in France after going to Disneyland Paris with his father.

He is crying and wants to come home… it’s Christmas on Friday and he wants to be at home Lauren Copping

They were due to travel back on Eurostar on Sunday night and were now trying to book themselves onto a National Express coach on Monday evening, she said.

She said Eurostar “had not helped them” despite several attempts to get information at the station, on the phone and online.

Ms Copping said earlier her son had been in tears when she spoke to him.

“He is crying and wants to come home… it’s Christmas on Friday and he wants to be at home.”

Airlines have stepped in to fill the gap caused by the non-running of Eurostar services.

British Airways said it was operating larger aircraft on many flights between London Heathrow and Paris on Monday, and Flybe said it was also increasing capacity to help ease the situation.

But EasyJet said French aviation authorities had imposed flight restrictions on the airline at Charles de Gaulle airport in Paris, leading to delays and cancellations.

On Monday morning some SeaFrance and P&O Ferries services from Dover were being delayed by bad weather in Kent.

But services with Norfolkline to Dunkirk, and LD Lines to Boulogne were running normally.