Fox said the "wild allegations" would be probed after confirming that he met Adam Werritty on an official visit to Sri Lanka in July despite previous denials his friend accompanied him on government business.
"I've asked the permanent secretary (his most senior official) to look into any of these wild allegations, and I'm very happy to stand by that investigation," the 50-year-old minister told BBC television.
The disclosure about the Sri Lanka trip followed the revelation that Werritty, 34, had visited Fox 14 times in 16 months at the Ministry of Defence in London, even though he is not a government employee.
Werritty had distributed business cards with a House of Commons logo and a description of himself as an "advisor to Rt.
Hon. Dr. Liam Fox MP", despite having no official role, the Guardian newspaper reported.
Fox said he had made it clear to his friend -- who was his former flatmate and best man at his wedding -- that it was "unacceptable to carry a card saying that he is a perso