“There are around two dozen proprietary names in the dictionary that are used in an extended or allusive way,” says Hughes. He highlights examples including Band-Aid, Biro and Scotch Tape or Sellotape.

But for brand owners, is this always a good thing? Aga, whose range cookers have been produced in Shropshire, England, since 1929, is the common word in Britain for any similar range cooker. Other manufacturers use the term “Aga-style” in their advertising, thus capitalizing on Aga’s reputation for quality and reliability.

Rebecca Morris, PR Manager for the Aga-Rayburn company, admits brand owners can only go so far in controlling use of their trademarks. Speaking specifically about Aga, she says there is little it can do about use of its name in reference to other range cookers, but adds that the company will act if the brand is treated detrimentally by competitors.

But in some instances careless talk can cost sales. SPAM luncheon meat became the butt of numerous jokes when it was satirized by the British comedic team Monty Python. In Britain, SPAM was associated with wartime food rationing and its adoption into the comic vocabulary coincided with – and some would say contributed to – declining sales. The last UK SPAM factory closed in 1997.

Subsequently, the word has taken on a new meaning as unwanted email. At first, SPAM’s trademark owner, Hormel Foods, resisted. It challenged junk-email entrepreneur Sanford Wallace over his registration of the domain name “spamford.com” and his use of the SPAM product in publicity photographs.

But ultimately the company admitted defeat. In 2000, it stated that it no longer objected to the alternative use of the word. Julie Craven, Hormel’s director of public relations, said the company was being pragmatic: "It certainly was at a point where it was becoming so much out there, and so much a part of popular culture."

Protecting one’s brand name once it has been let loose into the language might seem impossible, but it doesn’t stop trademark owners trying. Hughes is contacted several times every year by owners who want their brand’s definition changed in the OED. It is a pressure the dictionary resists. “Usually they want us to remove their brand or represent it in a certain way,” says Hughes. “If people talk about a trademark in a way thought improper, the owner may not like it but it is a fact. We record the word in the way it is used on a day-to-day basis.”

But there are instances when corporations have had success turning back the tide. The Rollerblade company acted when the media started to talk about “rollerblading,” promoting instead the term “in-line skating,” which is now widely used. Similarly, the Xerox Corporation prevented publications from using the term “xerox” in place of “photocopy.”

Motor manufacturer Skoda, meanwhile, used to be a byword for shoddiness and lack of style. When Volkswagen took over in the early 1990s, they decided to tackle the jokers head-on while openly admitting that the Skoda name can still be a problem. UK television commercials show buyers irrationally changing their minds at the last minute even though the facts about Skoda’s quality and reliability have been laid out for them. The direct approach seems to work, with Skoda’s UK sales in 2001 up 30% from 2000.

Stephen Gardner is a Brussels-based journalist and public affairs consultant.