Anyway, I decided I'd do some research. I downloaded the first build with speech recognition further up in this thread, and I've found the problem.
My language under "speech recognition" inn the settings was:
and notMicrosoft Speech Recognizer 8.0 for Windows (English - UK)
Changing this made everything start working, and the reason I detected it was because the earlier build states:Microsoft Speech Recognizer 8.0 for Windows (English - US).
This error just doesn't show up in the newer build.The language for the grammar does not match the language of the speech recognizer
So that's something you might want to look into. While I can use the US language (it works fine), I'd assume the UK language recognizer will pick up any particular differences in our languages.