World Cup migrant workers exposing exploitation are being identified by informants operating under cover within their camps, activists claim.

Researchers investigating migrants' conditions have found they are being quizzed themselves by workers on stadium construction sites in Qatar, The Mail on Sunday has been told.

The activists say questions were put to them in a formal manner that suggested their interrogators were professionally trained.

Equidem, the global human-rights and labour-rights organisation which works extensively in Qatar, has been told by sources that these under-cover security officials have been recruited in migrant workers' host countries...

'Our sense is it's being arranged by the government, not individual companies,' [Equidem Chief Executive Mustafa] Qadri said. 'But the companies may have their own people as well.