Philip Hammond has responded to a newspaper sting by The Sunday Times.
He told the The Andrew Marr Show: "I think the revelations are deeply damaging to the individuals concerned and their reputations.
"There is no way that retired officers influence the way in which military equipment is procured.
"I am satisfied that the system we have is completely robust.
"But there is an issue. Firstly over whether any rules have been broken. 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.
"Secondly we have to look at the level of access that we give retired officers to the MoD and to serving officers. "
More top news
No one gave him a chance - but Donald Trump has just pulled off one of the greatest feats in modern American political history.
German police are investigating an online picture thought to be of two British men doing a Nazi salute at a former concentration camp.
Late sunshine here and there this evening - but more cloud for southern Scotland, northern England and Northern Ireland again.