He said he would like to bring it back but there was little opportunity to do so.
Mr McDonald has continued to campaign for a ban and said he regularly gets young people telling him of having to do trial shifts and not being paid.
When his bill was blocked by the Conservatives at Westminster, he said: “The culture of unpaid work is a scourge on society and, the UK government must show its willingness to tackle this exploitative practice.
“Whilst the Tory government went out of its way to block previous legislation, there is a huge consensus across the country that unpaid trial shifts are pernicious and plainly unfair. Unpaid shifts serve as a blockage to those trying to find honest, paid work and must go.’’