Use of the word "apartment" in UK

Whenever I use the word “Apartment” using UK spellcheck, I get the following message: “The word “Apartment” is common for American English. Did you mean “flat”?”, I have clicked on “Ignore Rule”, and also added the word to my personal dictionary. However, I still get the error message every time I type the word. Any suggestions?

Do you think the rule is generally correct, and it’s only your personal choice to turn it off? If it’s not generally useful, we could turn it off for everyone.

Ignoring it will only work for the current text, the message will re-appear when you use it in a new text.

HI. Thanks for getting back to me. Although the word “Flat” is much more common in British English, “Apartment” is still a valid word used by many estate agents.