Each year scores of senior civil servants and ex-government ministers quit Whitehall for higher-paid posts in business. Companies in the fields of defence, health, energy and transport are particularly keen to recruit experienced politicians, policy makers and managers with close links to the wheels of power and procurement. This is the so-called "revolving door" between government and the world of commerce and industry. In recent years a free flow of talent both ways has been encouraged in the name of both efficiency and better communication between Whitehall and the wider world. But Government orders for goods and services are worth billions of £'s every year, and critics say the system is vulnerable to abuse and conflict of interest. For 'File on 4' Julian O'Halloran examines the effectiveness of the independent committee whose job it is to police the divide and protect the public interest.