Two of his aides have since been arrested as police and investigators examine deals and suspected kickbacks linked to the multibillion-pound event.

More than a million buy-to-let landlords, who have been battered by the devastating collapse in property values in the last year, face further headaches as investigators examine their tax returns.

The second method improves on the first by having investigators examine student or patient records looking for probable cases, to catch cases that have not been identified yet.