The general secretary of the RMT union has accused Transport Secretary Grant Shapps of “spouting nonsense” with plans to allow agency staff to step in for striking workers.

Mick Lynch criticised the proposed change in the law, which would allow flexible workers, including agency staff, to cover for those on strike.

Mr Shapps said the legislation change could be introduced within months.

Mr Lynch told the PA news agency: “Well, I don’t know how bringing in untrained, non-safety critical, inexperienced workers into a dangerous environment like the railway – with high speed trains, there are high voltage distribution systems, there are rules and regulations that have the power of statute – how that will help anyone, whether they are a passenger or a worker or manager or whatever?

“I don’t see how the use, the deployment of students or people who have got no work experience that are working for an agency will help anyone to resolve this situation, so as usual he’s just spouting nonsense given to him from some policy unit which doesn’t help to resolve the situations which are in front of us.”

Speaking outside London Euston Station, where he was joined by a number of striking workers, he also branded the plan to change the law as “draconian” and “a bit of an irrelevance” as it would not be possible to find agency workers to replace staff in “safety critical” roles.

He said: “They’re not going to be able to run 25,000-volt electricity control centres, they’re not going to be able to signal high speed trains, they’re not going to be able to maintain rolling stock and they’re not going to be able to drive trains, so it’s a bit of an irrelevance really to the situation that we’re facing,” he said.

“If he (Mr Shapps) wants to bring some people around and stand in empty stations to break strikes and pay them when he could be paying our members for a settlement, that’s something that he’s got to spend his time doing.”