An investigation has been launched by the Ministry of Defence after former military chiefs were reported to have boasted about lobbying top officials to secure contracts for private firms.

Defence Secretary Philip Hammond insisted the retired personnel wielded "no influence" over procurement.

However the body which restricts the commercial activity of departing civil servants said the allegations were serious as they are in breach of Whitehall rules.

Senior generals were among several ex-military figures recorded by undercover Sunday Times reporters posing as weapons manufacturers seeking to secure a multimillion-pound deal to sell hardware to the UK.