Controversial regulations which would have allowed employers in the rail industry to use agency staff during strikes have been banned by the High Court.

The rules were promoted last summer by Kwasi Kwarteng, who had been business secretary since January 2021 in Boris Johnson’s government. He said the reform would give businesses ‘freedom to access fully skilled staff at speed’ and was backed by the transport secretary Grant Shapps, who described the reform as ‘vital’.

Unions had argued against using temporary staff, partly because such a move amounted to ‘strike-breaking’ and also because many railway jobs need safety-critical skills.

The judge, Mr Justice Linden, said Mr Kwarteng had shown little interest in gathering evidence or any consultation, and that the government’s approach was ’so unfair as to be unlawful and, indeed, irrational’.

Mr Kwarteng had committed himself to changing the regulations even though ’the advice to him was that it would be of negligible short-term benefit and probably be counterproductive’, the judge continued.

The unions have welcomed yesterday’s judgment.

ASLEF general secretary Mick Whelan told the Guardian that the union was ‘proud to have stood with other unions to challenge these changes legally, and we will continue to do so in all those other areas, including minimum service levels, to ensure a level playing field for workers here in the UK’.

Unite general secretary Sharon Graham said: ‘The government’s decision to allow employers to recruit agency workers to undermine legal strike action was a cynical move to back their friends in business and weaken workers’ legal rights to withdraw their labour.’

The Department for Business and Trade responded: ‘We are disappointed with the High Court’s decision as we believed the decision to repeal the ban on agency workers covering strikes complied with our legal obligations.

‘The ability to strike is important, but we maintain there needs to be a reasonable balance between this and the rights of businesses and the public. We will consider the judgment and next steps carefully.’