LABOUR leader Sir Keir Starmer has reportedly ordered frontbenchers not to join picket lines outside stations as the UK faces the biggest rail strike in a generation.

But not everyone facing the demand has complied - with one parliamentary aide to the shadow Northern Ireland secretary openly defying the order.

Kate Osborne joined striking workers in Bromley, south-east London, saying: “I’m a trade unionist, I will always stand on the side of the workers.”

The Jarrow MP proudly shared a photograph showing her standing alongside railway workers.

Meanwhile, on Tuesday, one senior Labour MP warned colleagues that joining picket lines in support of striking workers will not resolve the dispute on the railways.

Shadow Treasury chief secretary Pat McFadden said he understands why the Rail, Maritime and Transport (RMT) union is pressing for a pay rise due to the rising cost of living, but that he wants to see a negotiated settlement.

The Conservatives have sought to use the row to claim Labour are on the side of the striking workers who have caused chaos for millions of commuters, and the Opposition leader is apparently reluctant to give the Government any more ammunition for that attack.

READ MORE: ScotRail services grind to a halt as Network Rail strikes start

Asked what his message to Labour MPs who do join the protests would be, McFadden told LBC News: “I would say to them, in the end that’s not how this will be resolved.

“It will be resolved by a deal that gets the railways running again, and that’s where the political focus should be.”

Asked if Osborne would face disciplinary action, McFadden told Sky News: “That’s a matter for the whips and for Keir Starmer.”

Sharon Graham, general secretary of the Unite union, said: “The Labour Party was founded by the trade unions and we expect Labour MPs to defend workers, by words and by actions.”

A number of Labour MPs posted on social media from picket lines as the strike got underway.

Ian Lavery, the MP for Wansbeck and a former Labour Party chairman, joined a picket in Morpeth, Northumberland, tweeting: “Solidarity with the @RMTunion today and all days.”

Former shadow cabinet minister Richard Burgon said: “We can’t just keep accepting workers’ wages and conditions being driven down so that the profits of the rich are driven up.”

Beth Winter, Labour MP for Cynon Valley, tweeted: “Complete solidarity with striking @RMTunion members today.

“The Trades Unions are the organised working class… the workers united will never be defeated.”

Birmingham Hall Green MP Tahir Ali said he would be joining pickets later on Tuesday and posted: “Solidarity to all those who are out taking action to protect jobs, ensure safety, and win better pay and conditions.”