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 in breach of Whitehall rules.

Defence Secretary Philip Hammond insisted the retired personnel wielded "no influence" over procurement but the body which restricts the commercial activity of departing civil servants said the allegations were serious.

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.

Among those named are Lieutenant General Sir John Kiszely, ex-head of the Defence Academy and now president of the Royal British Legion, former MoD procurement chief Lieutenant General Richard Applegate, Admiral Sir Trevor Soar, Commander-in-Chief Fleet of the Royal Navy until earlier this year, and ex-head of the Army Lord Dannatt.

The newspaper said its three-month investigation exposed claims of having pushed the interests of private arms firms despite being barred from doing so and of being able to push clients' interests to the Prime Minister and senior officials.

Curbs on the commercial activities of senior personnel when they leave public service are set in each individual case by the independent Advisory Committee on Business Appointments, based on rules set down by government.

A spokeswoman for the committee said: "We are drawing them urgently to the attention of ministers, the head of the civil service and the permanent secretary at the Ministry of Defence for them to consider what action they might take."

The committee has "no role or powers to investigate or sanction individuals who do not abide by its advice", she said.

The MoD said it was already looking into whether any rules had been broken and acting to ensure it was not possible for anyone to secure "privileged access". An MoD spokesman said: "It is clear that former chiefs acting in a commercial capacity should not have any privileged access to the MoD and we will be putting in place measures to ensure this."

In a statement Mr Hammond said: "Equipment is procured in the interests of our armed forces and not in the interests of retired personnel. Former military officers have no influence over what MoD contracts are awarded."