It has joined forces with a major trades union in an effort to stamp out "gang masters" who organise casual labour during the busy harvest months.

Between May and November each year up to 80,000 casual workers are taken on to work in the fields and orchards around Britain.

It is a traditional type of employment and is largely regulated and legal.

Supermarkets have pledged to play their part

But the Ministry of Agriculture is increasingly concerned about the 2,000 employers known as "gang masters" who strike deals with farmers to provide them with a force of casual labourers.

Their charges are often from eastern Europe, work in appalling conditions and are paid a pittance.

Meanwhile the gang masters take a cut of their wages and breach laws on tax, National Insurance, VAT and health and safety.

Under the name Operation Gangmaster, the government is planning a crack-down by mounting raids on farms this summer and autumn. The operation brings together the Ministry of Agriculture and the Department of Trade with the Transport and General Workers Union. Customs and Excise hopes to stop the evasion of VAT.