Apologies for the slow reply, seems I forgot to turn on email alerts.
No specific loudness requirements as such and no reason not to reduce the level into the limiter (which does reduce the number of artefacts, but does not eliminate them)
However, I would rather avoid any artefacts at all by dropping the entire output a couple of db for the DAB feed, and by 6db or so for the web stream (I would be aiming for about -14LUFS there).
Thanks for all your help this this by the way.