I have a pair of the twin dominator headlights that I want to dismantle, I've taken the bolts out of the bottom and side but the retaining ring and lamp don't seem to want to come away from the housing. Do I have to somehow split the two units from each other or just up the brute force?

Typical dally sorted it now I asked. Needed to prise them apart

I'd advise using an axe to split them to ensure you'll never be tempted to fit them afterwards

Why???