Is it possible to access HTML from BBC Basic so that the ORIENTATION could be lucked to landscape, as well as doing other stuff.
Locking the orientation to landscape is straightforward if you are creating a standalone Android application using my BBC2APK tool: it's documented in the help. I'm not sure what "other stuff" you are referring to however.
If you asking generally about the kinds of things that can be controlled using the Android Manifest, that's what the 'Custom Manifest' box in the BBC2APK GUI is for. But unless you are confusing HTML with XML (the manifest uses the latter) HTML is not involved.