I believe the issue is your default locale is not set to English (UK), which is the template you changed. When I explicitly set my browser’s locale, it loads as expected:
However, even if the default locale for the site has been set, the default language for the welcome page seems to be English (US). So when I replaced the English (US) text, then I could see the revised welcome text.
As you suggest, that default language seems to come from my browser (to which I have now added English (GB)).
Does this mean that, depending on the browser language of the visitor, they might see different texts? If so, then maybe I need to add the equivalent text in other languages our members are likely to have as default in the browsers, such as French or German.
Just to confirm that friends with non-English-language browser default languages can now see the intended English version of the text. So there was no need to add the equivalent text in other languages.