SNP MP Stewart McDonald has asked Tory chief Ruth Davidson to get her MPs to back his private members bill to ban unpaid trial shifts.

The Unpaid Trial Work Periods (Prohibition) Bill, which has the backing of the Scottish Trades Union Congress (STUC), the National Union of Students (NUS) and the Better Than Zero campaign, aims to end the practice of employers requiring job applicants to do an unpaid shift as part of the recruitment process.

While the UK government does not have official comprehensive statistics on the number of people being asked to work unpaid trial periods, a recent study by Middlesex University and Trust for London, Unpaid Britain estimates that workers are missing out on £1.2billion in wages.

McDonald has written to the party leaders in Scotland, asking them for support.

He said: “A fair day’s work deserves a fair day’s pay, but if my bill to ban exploitative unpaid trial shifts is to pass then it is vital that all of Scotland’s MPs get behind it, which is why we need to see a firm commitment of support from Scotland’s party leaders.

“Trial periods are used all too often by unscrupulous employers to take advantage of people who are desperately in need of a job, and use their labour for free without any guarantee — or even any intention — of an offer of paid work at the end of it.

“Since launching the bill I have heard from hundreds of people who have themselves been through this practice, and I cannot convey strongly enough the grim reality of what it is like for people to go through this kind of humiliating exploitation. It is a practice that belongs in the past and my bill offers some hope that it might finally be stamped out once and for all.

“SNP MPs will be backing the bill, and it has already received the support of the STUC, NUS, and the Better than Zero campaign, but the Tories, Labour and the Lib Dems have yet to say whether they will support it.

“I hope Ruth Davidson — and the other party leaders — will join the SNP in standing up for people in Scotland, by backing this bill to protect and extend the rights of Scottish workers and job seekers.”

Earlier this year, chef Mark Greenaway defended the use of the unpaid trial shift in hospitality, saying it should be regarded more as a “skills test”.

Greenaway, who holds three AA rosettes for culinary excellence said: “What we are talking about here is a skills test, which in our industry we call a trial shift.

“Working in a kitchen is not for everyone. I believe these trial shifts are more in favour of the employee than the employer.”