Richard Arthur, head of trade union law at Thompsons Solicitors, said: “There are very serious legal question marks around the proposals.

“The measures go further than the minimum service levels envisaged by the Transport Strike (Minimum Service Levels) Bill published in October. The Human Rights Memorandum accompanying that Bill set out reasons why minimum service levels were not justified in fire services, health settings and education and yet this is what is being proposed.

“The government is referring to minimum ‘safety levels’ and we anticipate legal challenge around what they are and who defines them.

“The introduction of minimum safety levels does not comply with the United Kingdom’s legal obligations under Convention No.87 of the International Labour Organisation on Freedom of Association and Protection of the Right to Organise, and Article 11 of the European Convention on Human Rights.

“The legal challenges when they come (and they will) are not something that the government can sidestep saying ‘Brexit has set us free’. The breaches will be of Conventions that the government has signed up to that come from the Council of Europe and the International Labour Organisation not the European Union.”