Britain's defence ministry said Sunday it would probe claims that retired military officers offered to lobby illicitly on behalf of arms firms, after high-ranking figures were filmed in a newspaper "sting".

The Sunday Times said a three-month investigation had revealed that four men were prepared to breach official rules in helping arms companies to access their high-level contacts in exchange for hundreds of thousands of pounds.

Ex-military officers may take on private sector work but are subject to regulations including a ban on lobbying for two years after they leave.

The report said two former top-level officers boasted of lobbying on multi-million-pound arms deals while they were barred from such work, while another said he would "ignore" the ban.

A fourth man offered to use his role at a military charity to lobby senior government figures at commemorative events for Britain's war dead, the report said.

The men boasted of close personal friendships with key figures in the ministry, which they indicated could help influence arms deals as they lobbied during informal meetings, the report said.

All four deny any wrongdoing, the Sunday Times said.

"We will be looking to see if any of these individuals have broken any rules," said a spokesman for the Ministry of Defence in a statement.

"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."

Defence minister Philip 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."

Britain has the world's fourth largest military expenditure, according to a report on 2011 spending by the Stockholm International Peace Research Institute.