Six Continents chief executive Tim Clarke has hit back at fierce criticism from Hugh Osmond.
The former Pizza Express and Punch Taverns entrepreneur has accused the 6C board of paying too much for pubs and a history of poor management, and of destroying shareholder value over the past 10 years.
"It just shows how little he understands running pubs," Mr Clarke told one Sunday newspaper. "Hugh is a very talented financial engineer and I have great respect for his skills on that front.
"But his understanding of day in, day out operating and building up of these kinds of managed pubs and his suggestions about our investment record couldn't demonstrate more clearly how little he understands the business.
"This is a business about brand management, about service, about the long-term building up of high sales and profit levels. It's not the business he's been in of rent collecting and contracting out to third-party lessees."
Mr Osmond's most scathing criticism has been reserved for the hotels operation.
Mr Clarke responded by saying: "It's just an extraordinarily opportunistic piece of timing to make a bid ahead of a Gulf war when the hotels are going through an incredibly difficult time.
"Fears of terrorism and of war have intensified recently - there is no more opportunistic time than that."
Mr Osmond, who also has a stake in Spirit Group, is trying to persuade shareholders to vote against a proposal to split the Six Continents hotels and pubs arms into two businesses.
He is thought to be prepared to improve his £5.6bn offer but only if demerger plans are postponed.