Next week’s rail strikes are “designed to inflict damage at the worst possible time”, Transport Secretary Grant Shapps said.

The Cabinet minister described the industrial action as an attempt to “derail reforms that are critical”.

Half of Britain’s rail lines will be closed during strikes on June 21, 23 and 25 by the Rail, Maritime and Transport union (RMT).

Transport for London (TfL) also “strongly encouraged” people not to travel on London Underground on June 21 because of a 24-hour walkout by the RMT and Unite.

The disputes have flared over pay, jobs and conditions.

In a speech at a train depot in north London, Mr Shapps said: “These strikes are not only a bid to derail reforms that are critical to the network’s future, and designed to inflict damage at the worst possible time, they are also an incredible act of self-harm by the union leadership.

“Make no mistake, unlike the past 25 years, when rising passenger demand year after year was taken for granted by the industry, today the railway is in a fight.

“It’s not only competing against other forms of public and private transport. It’s in a battle with Zoom, Teams and remote working.

“In case the unions haven’t noticed, the world has changed.”

Mr Shapps said rail strikes are “alienating” passengers and freight customers.

He issued an appeal to rail workers, saying he believes they are “less militant” than their union leaders.

“Don’t risk striking yourselves out of a job,” he said.

“Don’t pitch yourselves against the public.

“Let’s fix this situation and get back to building a better railway.”

Mr Shapps admitted the strikes are “going to cause misery”.

He said the Government is planning to introduce a “range of options” to respond to future industrial action, including the use of agency workers through legislation on transferable skills.

He explained: “People will be able to come where they have the appropriate level of skills, training and experience, and that is subject to a more straightforward secondary legislation process, so that would be very much quicker (than minimum service levels).

“If the strike drags on… then transferrable skills, sometimes called agency working, will be something which will become available as well in this particular dispute.”

He also said season ticket holders will be paid “full compensation on strike days”.

“I’ve moved to help make that an automatic process for those people in order to do whatever we can to remove the inconvenience for passengers,” he said.

This will be in place during next week’s industrial action.