Growing up in the 70s in the UK, a common brand of glue was UHU®1, and, at least at the time2, this was often advertised with the slogan "Don't say glue, say UHU".
If the phrase "Don't say glue, say UHU" were used by a competitor or the general public, I can see that it could be something a trademark owner might need to defend against (see Background below) as it seems likely to equate the two terms UHU and glue (whether as a noun, as a verb, or both).
Question: Is a trademark owner "immune" from "genericizing" their own trademark? Are they safe to use a phrase that, if used unchallenged by others, might dilute the protection offered to their trademark?
Note: I'm not asking whether this specific phrase would undermine the UHU trademark (if used by others); nor whether UHU's previous use of this phrase2 might have undermined their own trademark. Answers targeting UK/English law preferred.
If a company has a Trademark (™) or a Registered trademark (®)3, they have to take steps to protect it, or risk losing the protection that such marks offer. As well as guarding against direct infringements (a competitor using the protected mark on their own products), the other common area a company needs to defend against is letting the term pass into "common usage". As the article How to Protect Your Trademark From Infringement from the inc.com website says:
Many aspiring entrepreneurs dream of turning their brand into a household word. But watch what you wish for—if your trademark becomes the generic word for a kind of product, you could lose your ownership of it.
That was the fate of words like "escalator" (originally a trademark of Otis Elevator Co.), "zipper" (B.F. Goodrich), "aspirin," and even "heroin" (both Bayer AG). Today companies like Kleenex and Xerox struggle to avoid such a fate through marketing campaigns aimed at reminding the public that they are a brand, not a product category.
"The company most notorious for making sure you don't genericize their mark is Xerox, which insists that people use a Xerox copy machine, they don't 'make a Xerox,'" says Albert4.
The Wikipedia page List of generic and genericized trademarks includes lists of (a) former trademarks that have been genericized (where courts in at least some jurisdictions have ruled that the terms have become generic by becoming the common name of the relevant product or service); (b) former trademarks that have become generic for other reasons: typically through abandonment, non-renewal, or improper issuance (the generic term predated registration); and (c) protected trademarks frequently used as generic terms (e.g. Band-Aid®, Google®, Hoover® or Jacuzzi®) although still protected in some countries. Note: Many of the marks in those lists are still protected in some countries, even if declared generic in others.
From the above, it is clear that a company that wants to preserve the protections afforded to their trademark must defend against uses such as "I'll hoover the carpet" or "I'll just google that". "Don't say glue, say UHU" would seem (to me) to fall into the same category.
1 ®2019 Bolton Adhesives, part of the Bolton Group.
2 I've not seen any adverts for UHU for many years, so I do not know whether they still use the phrase. Their website (https://www.uhu.com), as of October 2019, does not appear to carry the phrase (a search returned no matches), and their current "tag-line" seems to be "glues anything, anytime". However, the UHU page on Wikipedia does claim it is their slogan (but with no citation), and this page on the trademark section of the Justia.com website indicates that "DON'T SAY GLUE...SAY "YOO HOO"" is a registered, and renewed, Word Mark owned by UHU.
3 Any trademark or registered trademark mentioned in this question is acknowledged as belonging to its owner, whether or not explicitly marked with ™ or ®.
4 Craig Albert, an intellectual property lawyer with Reitler Kailas & Rosenblatt in New York City. Quoted several times by the referenced inc.com article.