Walkouts by staff at two major rail companies threaten delays on South Western and Eurostar services as the UK faces travel meltdown.
Members of the Rail, Maritime and Transport (RMT) union working for both companies have walked out for 24 hours, mounting picket lines outside stations.
The walk-outs come as Eurotunnel passengers face long delays in Folkestone and air travellers face delays and cancellations at Stansted Airport due to “extreme weather” on the continent.
Eurostar station staff based at London's St Pancras claim they face "shocking and dangerous" working conditions because of repeated service failures and breakdowns.
The SWR strike is over the long-running dispute about the role of guards.
More strikes are being held in the coming weeks, including next Tuesday, following a walkout on Thursday.
SWR said it will run half its services on Saturday, advising passengers to check before they travel.
RMT general secretary Mick Cash said: "RMT members in the two separate disputes on Eurostar and South Western Railway are standing rock-solid this morning as they put the issue of public safety right at the top of the agenda.
"RMT Eurostar members have had enough of the company ignoring the dangerous overcrowding and appalling working conditions at St Pancras and our SWR members are continuing the fight to put public safety before private profit. That is the common thread that unites both these disputes.
"RMT is available for genuine talks in both the Eurostar and the South Western Railway disputes and it is down to the companies involved to get their heads out of the sand and get serious."
An SWR spokesman said: "It is frustrating and disappointing that the RMT union has decided to go ahead with plans to strike on our network.
"This is despite proposals we have put forward which are similar to that of another train operator, Greater Anglia, which the RMT has recently agreed to. We are urging the RMT to return to talks and end this damaging disruption to passengers.
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"We are sorry that this industrial action is inconveniencing many of our passengers, and will continue to do everything we can to keep passengers moving."
The union claimed the international terminal at St Pancras has been reduced to "chaos", with staff bearing the brunt of public anger over delays to services.
Around 140 staff are involved in the dispute.
Eurostar said it planned to run a normal service despite the strike.
