AN attempt to inflict a damaging parliamentary defeat on Theresa May has been launched by a Scottish MP in an audacious bid to force the DUP to break ranks with the Tories.

The SNP's Chris Stephens is to challenge DUP MPs to back a Bill on workers’ rights in the first test of the new parliamentary arithmetic at Westminster.

Stephen's proposed legislation is aimed at protecting those employed in the so-called "gig economy" by delivery firms like Uber and Deliveroo.

DUP MPs have vowed to back May in crucial Commons votes in exchange for £1bn of extra cash for Northern Ireland. The pact gives the government a notional Commons majority of six.

However, the pact does not cover employment law which is devolved to the Northern Ireland Assembly, although not to Scotland and Wales.

Stephens said his Bill represented a challenge to the DUP not to prop up the Tory employment agenda. Speaking to the Sunday Herald, he said: “In this house of minorities all these issues can be challenged and there is an opportunity for this to be the parliament that delivers social justice.

“There is a new opportunity, given the parliamentary arithmetic, to put forward a Bill that looks at workers' rights, especially in the so-called gig economy," he added.

Stephens said his Fair Rights at Work Bill will come before MPs after the summer break in an early test of the Tory-DUP arrangement. If the DUP's 10 MPs abstained or voted for Stephens' Bill, the opposition parties could defeat the government.

"Anything is possible", the Glasgow South West MP added when asked if the Tories could lose a Commons vote on the issue.

Last night, Labour's Shadow Chancellor John McDonnell suggested that his party's MPs would back the Bill from Stephens. McDonnell said: "This Bill largely replicates my trade union freedom Bill which was blocked by the Tories. The DUP MPs have to decide whether they represent the interests of their working-class supporters or represent the interests of the Tory Party."

Last week, a report for the UK Government by former aide to Tony Blair, Matthew Taylor, recommended that workers for firms such as Uber and Deliveroo should be classified as dependent contractors and as such receive extra benefits.

However, Stephens said that proposal did not go far enough and claimed his Bill would ensure that anyone doing paid work is treated as an employee with full rights to holiday pay and other benefits. He said his Bill would also make it easier for unions to win recognition agreements in the workplace.

It would replace the controversial Trade Union Act, that outlawed strikes not voted for by at least 40 per cent of eligible union members and where the turnout does not reach 50 per cent.

Stephens said: “The Taylor report did not go far enough, but this Bill will be an attempt to create fundamental rights at work. We have an opportunity to put forward a Bill and that’s what I plan to do to improve the rights of working people. It’s quite clear there is a public appetite for politicians to ensure that there are fairer rights at work."

Stephens is consulting the Institute of Employment Rights, a charity chaired by high-profile trade union lawyer John Hendy QC.

The SNP MP will now seek a parliamentary slot to introduce a 10-Minute Rule Bill, a procedure that allows backbenchers to introduce legislation.

The Scottish Trades Union Congress (STUC) has also thrown its weight behind the challenge to the DUP. The STUC said the DUP would be under pressure not to oppose the Bill as it is an area of legislation that is devolved to Stormont. It also pointed out that the DUP did not vote to pass the Trade Union Act in the last parliament.

STUC general secretary Grahame Smith said: "It is notable that the DUP and Conservative Party agreement does not include areas which are reserved to the Northern Ireland Assembly. From the perspective of workers who have seen their rights systematically dismantled over the last few decades, this is an important fact. The Tories had a wafer-thin majority for the Trade Union Act with DUP politicians not voting on the final act. If they were to repeat this decision in the current parliament, the majority for restricting trade union freedoms would likely dissolve.

"Similarly, with the Tories likely to bring forward legislation on the recent Taylor Review on employment in the gig economy, there would not be a majority for actions which fell short of protecting those workers.

"Employment law is devolved to Northern Ireland. However it is not covered by EVEL (English Votes for English Laws) because employment law is not devolved to Scotland or Wales. It would be ironic indeed if DUP members were to vote on an issue not affecting their own constituents in a way which contradicted the wishes of the Scottish and Welsh electorates which would be affected by such a law.

"Equally, it is far from clear that the DUP would be minded to vote against more progressive employment protection. Large swathes of their constituents lack the protections of the right to proper union activity and protection against precarious work.

"If Labour, SNP or other parties chose to bring forward legislation to increase workplace protection the DUP would be faced with a choice on whether to prop up the Tory employment agenda or defend the workers they represent."

In response to Stephens, a UK Government spokeswoman said: “British business is successful at creating jobs, enhancing earning power, and improving life chances across the UK. Employment rates are the highest since records began, and minimum wage rates have never been higher."

The Sunday Herald approached the DUP for a comment but they didn't respond before publication.