An anti-strikes Bill could cause the number of industrial walkouts to increase, according to an impact assessment released by ministers.

An analysis of the Strikes (Minimum Service Levels) Bill published on Tuesday said unions could seek to “maximise their leverage” by balloting for strike action in the run-up to the draft law being passed.

It went on to suggest that the proposed restrictions on strike action could sour the relationship between unions and employers to such an extent that there could be an “increased frequency of strikes for each dispute”.

The assessment released by the Department for Business and Trade said “action short of striking” could also be approved in the sectors covered by the Bill’s scope.

The Government is attempting to introduce legislation setting out minimum service levels during strikes across six sectors, including transport and health.

The impact assessment said the policy “could mean a general increase in tension between unions and employers”, adding: “This may result in more adverse impacts in the long term, such as an increased frequency of strikes for each dispute.”

But the assessment goes on to say that such an outcome was “very speculative”, even arguing that minimum service levels (MSLs) could lead to unions settling “more quickly than they may otherwise would have”.

In the short term, department officials said there is also the risk that unions would look to ballot for more strikes in the run-up to minimum service levels becoming law.

The document said: “There is a potential increase in strike action prior to MSLs being introduced as unions may seek to cause disruption which is not mitigated by an MSL before they are implemented, in order to maximise their leverage.

“This risk may be mitigated by the costs to unions and their members, principally loss of pay, of taking industrial action.”

The impact document also found that non-strike related action could become a popular form of lawful protest once the anti-strikes Bill enters British statute books.

The action “short of striking” is thought to include tactics such as work-to-rule, where staff refuse to work overtime.

Such a development could have a “significant negative impact on the level of services provided” in sectors which are “reliant on staff working additional hours”.

Non-strike industrial action would be able to continue even when minimum service levels are being enforced, it added.

“It could be that instead of taking strike action, action short of a strike becomes a more prevalent form of lawful protest,” the department said.

“Although hard to quantify, this is likely to be less disruptive than industrial action without MSLs in place.

“It may nevertheless lead to a prolongation of the dispute.”

UK Government ministers argue the minimum service levels policy will bring Britain into line with other nations and help protect the public from the impact of strikes.

The publication of the impact assessment comes as the Bill has progressed through the House of Commons.

It was due to receive its second reading in the Lords on Tuesday.

The Regulatory Policy Committee (RPC), the independent watchdog for regulations, said the impact assessment published by the Department for Business and Trade was “not fit for purpose”.

The 10-page report, dated Monday February 20, found that some sources for the cost-benefit analysis were “almost a decade old”, while also suggesting that there were a “number of assumptions made” without giving “appropriate evidence and analysis”.

It added: “The department includes a sizeable section in the IA (impact assessment) setting out potential risks arising from the policy, which includes the acknowledgement that the intervention may lead to further strike action.”

Unite general secretary Sharon Graham said the anti-strikes Bill was a “total ‘dog’s dinner’ which will only inflame and prolong disputes”.

On the RPC handing the impact assessment a red rating, she said: “Now we can see that it has been so badly thrown together that it has received the worst verdict of any draft law that anyone can remember.

“The Government needs to stop wasting time with its attacks on workers’ rights and focus on resolving the issues behind the current wave of strikes.”

Deputy Labour leader Angela Rayner, also commenting on the red notice, said: “Tory ministers have failed utterly to do due diligence on this shoddy, unworkable policy – breaking their own rules and failing to provide evidence for their claims.”

Downing Street, asked about the impact assessment, said it thought the legislation amounted to a “legitimate approach” to ensuring public safety during walkouts.

“We think these proposals are not just appropriate but a proportionate response to protect life and health during industrial action,” said the Prime Minister’s official spokesman.