The treatment of seasonal workers looks set to come under closer scrutiny next year as the Gangmasters Licensing Authority steps up the number of unannounced visits it carries out.

More inspections and more staff were among the recommendations made in the GLA's first annual performance review, conducted by the Universities of Sheffield and Liverpool.

Overall, the GLA had done "a good job in a challenging environment", said researchers, but there was still much work to be done.

They called on the GLA to request more industry intelligence from labour providers, labour users and retailers, and also proposed the creation of an undercover task force. This could be done in collaboration with HMRC or the police.

Researchers also identified a need to tackle "dodgy and criminal gangmasters who lurk behind the scenes of licensed labour providers" and who bring the GLA licence into disrepute.

The report has been broadly welcomed by the multiples, which said they would discuss the recommendations with the GLA in the new year.

The GLA said it had already been working to ensure contracts and workers' terms and conditions were now more transparent, health and safety at work was taken more seriously, minor worker abuses such as wage deductions had been reduced, and substandard accommodation was not so prevalent.The GLA has so far revoked 36 licences and refused 32.

"We know exploitation still exists in these very competitive industries and it is a challenge that needs an industry-wide effort," said GLA chairman Paul Whitehouse. " We need to demonstrate our capacity to ensure protection for workers and a level playing field for legitimate businesses."

NFU chief horticultural adviser Philip Horton echoed Whitehouse's call for an industry-wide effort.