Immigration officers this week arrested 12 suspected failed asylum seekers working on a £560m Ministry of Defence construction project, in what is believed to be part of a wider crackdown on illegal workers in the industry.

The workers were arrested on Sir Robert McAlpine’s Colchester army barracks project in Essex, while working as labourers on the site. It is not known which of the project subcontractors had hired the labour.

A source close to the raid said that the Home Office was stepping up its activities on construction sites, and that officials had recently visited sites and shown contractors typical examples of forged documents.

A Home Office spokesperson refused to discuss the operational details of its activities.

Intelligence-led operations are going on across the country

Home Office spokesperson

n About 20 electricians on the Heathrow Terminal 5 project have been suspended and the police called in over allegations of criminal damage on the site.

Building understands the men had been made redundant by contractor Sepam, a decision contested by Amicus. Sepam then alleged that the men had caused criminal damage. All workers concerned have been suspended, and a meeting between BAA, the workers and police was due to be held yesterday.