Private policing is a boom industry. Forces around the country are seeking to slash costs in the face of 20 per cent budget cuts demanded by Government, and outsourcing to the private sector is the preferred means of trying to balance the books. But the country's most senior police officers are facing increased scrutiny amid growing disquiet over the "revolving door" that has seen chief constables join security firms scrambling multibillion pound private contracts.

MPs are to examine the need for a register for senior officers joining the private sector, reflecting growing concern about the potential for conflicts of interest, as private companies look to retiring, middle-aged officers for help in chasing lucrative contracts to carry out police duties. Tomorrow, the potential for even serving officers to be lured to the private sector will be raised at the Home Affairs Select Committee.

It has emerged that the biggest private policing deal to date saw rival companies with two former heads of Scotland Yard on their boards vying for a £200m, 10-year contract to replace traditional policing jobs in Lincolnshire.

The tender was won by the world's largest security company, G4S, whose board includes the £125,000-a-year deputy chairman and former head of the capital's police force, Lord Paul Condon. Lord Condon was not part of the bidding team.

G4S led a shortlist of five companies which included a consortium of Capita, Mitie and BlueLight Global Solutions, chaired by Sir Ian Blair, who left the top job at the Met in 2008. Two former chief constables, including chief executive Bob Quick, and the former head of the Serious and Organised Crime Agency are also on BlueLight's board. At the Leveson Inquiry last week, Sir Ian referred to the "oddity" of people being able to join a firm bidding for work at their former organisation. He raised the possibility of a two-year cooling-off period. Mr Quick said that there could could be a perception of undue pressure if a senior officer left a force to bid for a project to supply it. "Even if it wasn't true, it can create that perception," he told The Independent. "It's only right and proper that all of that is looked at across the whole commercial sector."

A third former commissioner, Lord John Stevens, who served from 2000 to the end of 2005, is on numerous boards of companies mopping up traditional policing services. They include the biggest private forensic science laboratory, whose workload has increased with the closure of the state-run provider. Poaching police officers is a tried and tested business strategy. The generous terms of the police pension means that some can retire as early as 48 with a full pension and still work.

Private provider Steria said that it had transferred 500 civilian staff from Cleveland Police to its books including a number of retired police officers to carry out a £175m 10-year contract. Steve Matthews, the chairman of the Cleveland Police Federation, which represents rank-and-file officers, said: "I think there should be at least two or three years [gap]. I think it's inappropriate coming back working for that company."

Although there is no question of any wrongdoing, the Home Affairs Select committee will make the migration of officers to the private sector a "central part of our inquiry into leadership and standards in the police". The chairman, Keith Vaz, said the committee would consider creating a similar system for former police officers as exists for former government ministers, prevented from lobbying for two years. They must consult with an independent panel before taking up jobs in the private sector.

Mr Vaz said: "To avoid doubt, an open register could be introduced and the template already in place for former ministers could be adopted." The contract for the Lincolnshire project also allows 10 other similarly sized forces to purchase the same services from G4S, potentially worth £2bn, without going through a separate tendering process, and increasing its grip on British policing. Lincolnshire will act as the "broker", eligible for a payment in each deal.

G4S already manages 30 custody suites in Lancashire, South Wales and Staffordshire, provides forensic medical services and has 20,000 former police staff on their database which has been used by more than 40 forces. It is in discussions with a number of other forces, The Independent has learned.

A G4S spokesperson said: "We would support any moves to introduce a cooling-off period for retiring senior police officers before they join private companies. This seems entirely sensible.

"Lord Condon's role as senior independent director of G4S means he has no involvement with individual contract negotiations. We actively seek to avoid conflicts of interest, and our contract with Lincolnshire Police has an exclusion clause for senior police staff of one year." The West Midlands and Surrey police forces also plan a £1.5bn contract for services, which includes a role in criminal investigations.

The proposals have raised concerns among rank-and-file officers about private staff taking jobs. The police watchdog, the Independent Police Complaints commission (IPCC), has no automatic jurisdiction over privately contracted staff. Surrey Chief Constable Lynne Owens told staff: "Any suggestion that a private sector company will patrol the streets of Surrey is simply nonsense."

Dr Adam White of York University, author of The Politics of Private Security, said the industry had for years poached officers to enhance its "public legitimacy" and aid its expansion. "It also helps them connect to the old-boy network which helps pick up contracts."

Stuart Lister, senior lecturer in criminal justice at the University of Leeds, said: "The reforms will bring the potential for conflicts of interest into much greater focus."

Case study: The private-sector firm and a death in police custody

Sharon McLaughlin, 32, died from a "cardiac event" in Worthing Custody Centre in May 2010. She died alone in a cell, probably in drug withdrawal after spending nearly 24 hours in custody for allegedly shoplifting to feed her heroin habit. Officers found dozens of used needles and drug paraphernalia during a strip search, yet there was no mention of her addiction in the initial risk assessment. Sussex police custody suites are staffed by Reliance Security, which is not accountable to the IPCC.