Ex-military chiefs may be barred from contact with ministers and Ministry of Defence officials after several were secretly filmed claiming to be able to help secure deals for arms firms.
At least one of the six top figures filmed by The Sunday Times was still subject to the two-year lobbying ban imposed on former military personnel leaving public service, Defence Secretary Philip Hammond said.
The rules state they cannot become involved in any activity which might be helped by their previous role for those two years.
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.
Mr Hammond said any breaches of the lobbying rules would be investigated.
He also said the revelations were "deeply damaging to the individuals concerned and their reputations" but insisted there was "no way that retired officers influence the way that military equipment is procured".
Instead, he said those filmed were "rather bigging up their capabilities" and showing "bravado" to impress.
But the rules appeared to have been broken and may need tougher enforcement, Mr Hammond said.
"There are many, many reasons why it is sensible for the MoD to maintain contact with retired officers," 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."
Labour has called for an investigation into the paper’s claims.
Shadow defence secretary Jim Murphy said: "These are grave allegations that have to be fully investigated. We need to know every detail, every meeting and every contact between those recorded in this video and those still serving in the MoD."
One of those accused by The Sunday Times was Lord Stirrup, who was alleged to have boasted that he had "old friends" in the MoD who would help in a lobbying campaign to win defence contracts. Lord Stirrup himself was not accused of breaking the two-year rule.
But the former chief of Defence staff told Sky News he was never paid to lobby MPs on behalf of arms firms .
He told the Murnaghan programme that he and his retired colleagues were only ever used for their expertise, not their influence.
"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 also said, which was not reported, was that approaching ministers is not the way to do it... you need to understand the military's requirements, and they're not set by ministers."
Others senior military figures filmed by the paper were 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.
All deny breaking any rules, the newspaper said, and insist they had the best interests of the military at heart.
