they are the domed ones, with a chrome ring 7 rubber by the look of it, they seem to twist but the rubber is pretty degraded so dont want to force them for fear of not being able to put them back
It's a Traveller isn't it?
So basically what Peetee said. You'll need something like a screwdriver but without sharp corners on the blade to prise the rubber off the chrome ring as it's easy to nick/damage 40-year old rubber. Got a miniature tyre lever handy?
Yes, the glass is held in by a lip on the rubber seal, and the lip is prevented from moving by the chrome ring, so you have to prise the chrome out before the glass.
Alex Holden - http://www.alexholden.net/
If it doesn't work, you're not hitting it with a big enough hammer.
Blunt small screwdriver as already suggested - ease it in under the outer edge of the chrome ring and then run it around to pop the ring out. The beehive glass will then come out easily enough. New rubber boots are not expensive. Glass beehives are far better than later plastic copies! I fitted 'chrome plastic' collars around the bulbs which have approx doubled the light output seen from the lamps!