Gangmasters behind "wholesale" exploitation of illegal immigrant workers would face automatic jail terms under a Labour government, the shadow home secretary said yesterday.

In a speech outlining Labour's approach to immigration, Yvette Cooper called for minimum jail terms for sweatshop owners and gangmasters.

She also unveiled plans for a consultation on revising the existing criminal offence of forced labour to increase prosecutions.

Current law requires an element of coercion or deception between the defendant and the victim, such as poor accommodation provided by the employer.

Ms Cooper claimed these laws have failed.

She said: "The truth is that for too long exploitation in the labour market - a cause and effect of low-skilled immigration and illegal immigration - has gone unchecked.

"We want clearer, stronger laws so businesses know where they stand and responsible employers know they won't be undercut, but also so that it is clear that employers who use pressure or force to exploit people and get round employment law are committing a crime."

In an effort to strengthen labour exploitation enforcement the government said on Wednesday that the Gangmasters Licensing Authority (GLA) will be moved the Home Office in order to work alongside the National Crime Agency.

It claimed this would strengthen the GLA's "enforcement and intelligence capabilities."

The announcement drew fire from unions who said it was a mistake.

Construction union Ucatt believes that the GLA's focus will be diverted from concentrating on labour exploitation to issues of law and immigration enforcement.

The union says that vulnerable communities will lose trust in the GLA and workers will be less likely to raise concerns for fear that they could be incriminating themselves or their colleagues.

Ucatt general secretary Steven Murphy said: "The GLA is recognised as doing an excellent job in preventing exploitation in the sectors it represents, as it is seen as being on the side of workers."

General union Unite assistant general secretary Diana Holland warned the move was a smokescreen by the Tories to cover up their attacks on workers' rights.

She said: "The GLA has been hampered by this government. Last year, ministers 'deregulated' the legislation to ensure that first time licence applicants escaped inspection.

"This was playing fast and loose with worker safety to save business the inconvenience of having to demonstrate it is law-abiding."