Retired military officers have been secretly filmed claiming they can influence arms deals worth millions of pounds.
The Sunday Times claims the results of a three-month investigation have revealed that several former military generals are available for hire as lobbyists, despite official rules banning the practice.
Reporters posed as representatives of arms firms and arranged meetings with former top military figures and recorded them offering their influence and contacts with ministers and in return for six-figure sums.
The rules governing lobbying by former military personnel stipulate there must be a moratorium of two years before they can become involved in any activity which might be helped by their previous role.
Former chief of defence staff, Lord Stirrup, was accused by the paper of boasting that he had "old friends" in the MoD who would help in a lobbying campaign to win defence contracts.
But he told Murnaghan on Sky News he was never paid to lobby for defence contracts.
"I was asked about my contacts. If you're pressed about them then of course you say what they are,” he said.
"I was asked about whether I know ministers - and I do. What I was also said, which was not reported, was that approaching ministers is not the way to do it... you need to understand military's requirements, and they're not set by ministers."
According to the paper, Lieutenant General Sir John Kiszely, former head of the Defence Academy, claimed he could use his role as president of the Royal British Legion to influence his clients' agenda with the Prime Minister.
Lieutenant General Richard Applegate, a former Ministry of Defence procurement chief, reportedly described a secret lobbying campaign in parliament for a £500m military programme on behalf of an Israeli arms company.
The paper claimed Lt Gen Applegate was prohibited from lobbying at the time because he had recently retired.
It was also reported that Admiral Sir Trevor Soar, Commander of the naval fleet until March 2011, told undercover reporters he would "ignore" the two-year ban imposed on lobbying ministers.
Lord Dannatt, the former head of the army, also talked about ignoring a ban on discussion of a £400m contract by "targeting" the MoD's top civil servant, with whom he went to school.
Lord Dannatt, who was an adviser to David Cameron before the 2010 election, said he offered to "facilitate conversations" but rejected an £8,000 monthly fee offer.
When confronted by the paper, the men strongly denied having breached any rules. They added their actions were motivated by having at heart the best interests of the armed services.
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.
In a statement, the Ministry of Defence said: "We will be looking to see if any of these individuals have broken any rules.
"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.
"A rigorous process is used for the approval of all equipment projects which involves non-advocate scrutiny of all major investment decisions by an investment approvals committee which provides advice to ministers and the accounting officer."
Defence Secretary Philip Hammond denied former military personnel were able to use their contacts to influence arms deals.
But if any ex-officers were found to be, Mr Hammond said he could "shut down" their access to ministers.
"There are many, many reasons why it is sensible for the MoD to maintain contact with retired officers. They are often asked (by the media) to comment on things that are going on in the defence area," he told BBC1's Andrew Marr Show.
"But if they are abusing that access for commercial purposes then we will have to tighten it up or maybe even shut it down. That is something we will now look at.
He added: "Clearly at least one, possibly more, of the individuals named in the Sunday Times piece were still under the terms of the two-year restriction that applies after they have left the service.
"If we find that people are not abiding by the advice they are given then we will need to look at whether there are steps we can take to shut down their access to ministers and officials."
Mr Hammond also issued a warning to arms firms that engaging in such lobbying would backfire.
"If we were to make clear to companies that the kind of lobbying being talked about here will damage them rather than benefit them, that will be quite effective."