Labour MPs were out celebrating with union bosses from the Aslef union, while Britons battled disruptions on their rail networks.
Union boss Mick Whelan hosted more than 100 members, along with several Labour MPs, for a gathering in a ballroom at the Earl of Doncaster Hotel.
Guests included Labour MPs Ian Lavery, Grahame Morris, Ian Mearns and Kate Osborne.
Osbourne posted a video of Whelan handing her a gift and pulling crackers on the same unions introduced an overtime ban for rail services.
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Alongside the clip, Osbone said: “Great to be with Aslef comrades in a womderfully (sic) Christmas venue and solidarity to all those taking strike action today.”
Pictures of the event, acquired by the Sun, show people crammed into the decorated ball room for the festive gathering.
Hundreds of trains have so far been cancelled as a result of the nine-day industrial action, which began three days ago.
Hitting out at the event, Transport Secretary Mark Harper said: “While Aslef bosses have lavish parties with Labour MPs, they remain intent on causing more disruption with strikes targeting working people who could only dream of a train driver’s salary north of £60,000.”
Meanwhile, Tory MP Greg Smith accused the unions of “laughing in our faces at swanky dinners”.
The ballroom at the Earl of Doncaster Hotel costs £4,000 to hire.
A source told the Sun the event was Aslef’s Christmas party, adding: “They were having a very good time.”
But Aslef rejected characterisations of it as a party, saying: “There was no music, no disco, no karaoke, and no dancing.”
It added: “It was an annual lunch to commemorate those people we have lost in the last 12 months and to look ahead to what we hope to achieve in the next year.”
Aslef is currently embroiled in a prolonged dispute with 14 train operators across England.
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Speaking about the fresh round of walkouts, Whelan said: “We have, in the past, called everyone out on the same day; by spreading the strike action, for which members overwhelmingly voted, coupled with our ban on overtime – action short of a strike – across the week, the ramifications for the rail industry will be greater.”
The industrial action began just hours after the Rail, Matitime and Transport Union (RMT) paused its dispute after members voted overwhelmingly to accept a no-strings pay offer withbfurther negotiations in the New Year.
