On 6 Sep 2019, at 7:20, Carpii UK wrote:
I'd already tried that but came to the conclusion you couldn't do it for files without an extension
It turns out it was an issue with PathFinder Desktop (which I forgot replaces many aspects of Finder).
Well hey, if you’re using Path Finder anyway, you can just add “Open in TextMate” to the top-level of the contextual menu for all files. I did this long ago.
In the Preferences, go to Features → Contextual Menu.