Media playback is unsupported on your device Media caption Meghan Wright from Edinburgh says trial shifts took advantage of her

Some MPs and lawyers have called for a blanket ban on unpaid shift work.

Companies can currently invite prospective employees to do trial shifts with the carrot of a job at the end.

But there has been a six-fold increase over three years in complaints over unpaid shifts, trade union Unite said.

The Federation of Small Businesses said unpaid shifts are a valuable part of the recruitment process, but shouldn't cross the line into exploitation.

On Friday a private members bill which seeks to make unpaid trials illegal will get its second parliamentary reading.

Job promise

Meghan Wright's first experience of an unpaid shift was with Nando's in 2014.

"They told me it was six hours, and I'd get a meal at the end.

"I assumed I'd be observed and trained but I was meeting and greeting guests, taking orders and clearing tables. I was basically working as a staff member."

She had a similar experience working at a supermarket crèche.

"When it came to the full-time staff's lunch break they asked me to stay to cover it. The worst thing about that was that I never heard back from them - even though they promised I'd be offered the job."

Nando's told us: "We do invite potential team members to shadow a member of the team during a four hour trial shift. Whilst these trials are unpaid we will always offer a meal and feedback."

Unite says that too often, "shadow shifts" are crossing over to labour and exploitation.

They claim they've gone from receiving around three complaints a week, to up to twenty.

Stewart McDonald, the SNP MP for Glasgow South who tabled the private members bill, says current legislation - which bans "excessively long" trial shifts - is not working.

"People are being asked to try out for jobs that don't exist.

"Companies are just trying to cover staff absences in other parts of the business.

"This is about ending that exploitation and empowering applicants and making sure there is dignity throughout the process," Mr McDonald said.

There is nothing illegal about asking a worker to do a voluntary trial shift.

Smaller businesses in particular rely on them as part of the recruitment process.

Image caption Colin Borland from the FSB says small firms find trial shifts useful

Colin Borland from the Federation of Small Businesses said: "Small businesses can sometimes be reticent about hiring or even looking to expand headcount when the work is there because they are worried about making the wrong decision.

"The more that we can do to make sure that they hire the right people the better. You just have to be very careful that it doesn't cross into what's exploitative."

Is it always possible to identify when the line has been crossed?

Unpaid work is in theory voluntary, and so some argue that legally negotiating payment is a grey area.

Lois Madden, an employment solicitor in Edinburgh, doesn't agree.

"There is nothing grey about this.

It's illegal to ask someone to come in, to give up their time, to provide services, to provide revenue, and not pay them at least the minimum wage, or the national living wage if they are over 25," she says.

The legal advice for prospective employees is to outline the terms of the trial shift before it begins, and question anything over a few hours.

But Meghan and many others say in reality that can be tricky; it can feel as though you're jeopardising your chances if you challenge your potential employer.

"As long as everyone's doing it, nobody wants to be the first to stick their neck out," Ms Wright says.

"There are more people than jobs, and if someone says you have to do a trial shift, you don't want to say no."

Which is why some MPs and lawyers say a blanket ban is the only way to robustly prevent exploitation.