Justice secretary, Robert Buckland has said it may be legal for companies to make Covid vaccine a condition of employment at least for new employees but unlikely employers make it compulsory for existing workers under their current contracts.

Downing Street has said it would be “discriminatory” to order people to be vaccinated to keep their job as some firms say they will not hire new staff who refuse to have the jab.

In an interview on ITV, Buckland said compelling new staff to be inoculated could, in theory, be possible if it was written into their contracts however, employers would probably need to take legal action if existing staff refused such an order.

“I think that has to be the case because we’re dealing with existing terms of contracts of employment, thousands of existing contracts,” he said.

He added that the legality of “no jab, no job” would depend “very much on the terms of employment and the particular contract”.

“Generally speaking I’d be surprised if there were contracts of employment existing now that did make that approach lawful. I think frankly the issue would have to be tested.”

David Samuels, legal director at law firm Lewis Silkin, said that there is nothing legally to stop a business from placing a “no jab, no job” clause in contracts for new hires, however, employers would need to analyse each job role and evaluate health and safety risks before introducing such a clause.

Failure to do so would make it possible to challenge a contract as being unfair or discriminatory, if a claimant can prove they are exempt from having the vaccine for some reason, or unable to access it.

The prime minister’s official spokesman has said: “Taking a vaccine is not mandatory and it would be discriminatory to force somebody to take one.”