JOHN McDonnell has pledged to join rail workers on the picket line after a union chief raised the prospect of a winter of discontent on Britain’s railways.

The Shadow Chancellor was responding to a warning by Manuel Cortes, the TSSA General Secretary, who told the TUC Congress in Manchester that widespread industrial action across the UK's rail networks was on the cards if the threat of “wage cuts” to staff by Chris Grayling, the Transport Secretary, was not neutralised.

Mr Cortes has written to the Train Operating Companies, including ScotRail, and to Network Rail seeking assurances they will not support Mr Grayling's move to impose pay rises which fell below the normal Retail Price Index, which, he argued, would be an effective pay cut.

Noting how morale among overworked rail staff was low, the union chief said they were furious with the Secretary of State’s plan.

“Unless he backs off or, better still, is booted out, industrial action including strikes this coming winter loom large,” declared Mr Cortes.

He said the TSSA union would seek support from Congress to send a message to “this dysfunctional Tory government, that if they try to take on rail workers, the full weight of the Trades Union movement will be behind them as they bring our railways to a halt this winter to hold Chris Grayling and this lamentable government to account".

Mr McDonnell, whose keynote speech to Congress pledged to give workers in the gig economy the same rights as other employees, including sick pay and parental leave, said he recognised there was “real anger” among rail workers.

Asked if industrial action was something he would support, the Shadow Chancellor replied: “We will see what industrial action takes place. I’m hoping there will be negotiated settlements. But don’t underestimate the depth of anger among railway workers at the moment.

“If there are ballots for industrial action and the management aren’t responding accordingly, I will be on the picket lines with the workers themselves.”

He added: “The management in these individual companies now need to start waking up about just...what’s happened with railway workers' standard of living and how they feel their professionalism has been undermined.”

Meanwhile, TSSA said it had notified ScotRail of a ballot of its members for industrial action in a dispute over payments for rest-day working.

The union said its members were seeking parity with ScotRail drivers, who currently received a payout of £300 for every rest-day they worked, which it noted was significantly more than TSSA members.

Mr Cortes said: “Rest-day working payments are paid to staff to compensate them for giving up a day’s rest to keep our railway running. Our railways need more than train drivers to run. Our members in ScotRail keep trains running safely from the control room and they also make sure that passengers are safe and informed. ScotRail are treating our members as second class citizens...We aren't asking for the world, all we are seeking is parity.”

The union leader noted how, without the goodwill of ScotRail staff working on rest-days, then the company would “find their trains idling at the platforms because they can’t run them without our members authorising their departures”.

Mr Cortes made clear the TSSA’s door was open to talks with ScotRail management but added: “Our members won’t be putting up with second class payments for first class work any longer.”