Does anyone know a company that could make me small quantities of a double walled tube? The first (inner) tube to be 1.5-2mm wall, clear resin with a single layer of 80gsm woven glass fibre (preferably as close to the inside of tube as possible), the outer tube to be “normal” carbon fibre with standard 1.5mm wall and the outer diameter to be 25mm.

Odd request I know...but then I did say I was the mad scientist...

The Problem will be to her a 1,5mm thickness with only a single layer of 80g glass in it

That’s interesting actually...how many layers of weave are in a normal 1.5 mm wall tube?

The problem is, that composite tubes (not the pultruded ones, they are are made completely different) of that diameter are usually rolled prepreg over a steel mandrel. The consolidation is achieved by wrapping it in plastic tape. So there would be two problems: first, to get hands on a small quantity of 80g glass prepreg. Secondly, to get it heated (with additional epoxy film) in a controlled way, so that the resin will not bulk up in some places, and produces an uniformed wall thickness.
A single layer of 80g glass will be around 0.05mm in thickness.
The question is why do you want such a tube? Would a tube with a 2.95mm carbon and 0.05mm glass wall thickness suit your needs? I am guessing it's a matter of electrochemical insulation?

More mundane than that...I’m looking for something translucent within something opaque (and aesthetically pleasing) with high rigidity/strength. It’s possible that more gf weaves would still be light transmitting, but at present I don’t know.

I want to light the tube internally, having etched away a design in the outer CF layer. This of course reduces the strength considerably (depending on the design) so this needs to be compensated for by the internal gf tube, which also acts as a screen...as some strength is still required.

What about an acrylic tube? You would need 19x22, I found 18x22 within a quick search of 10 sec. Key it, and wrap carbon around it. Prepreg might exceed the thermal specs of acrylic, but it should be no problem to find somebody, who can do an infusion around the tube for you.

I already tried a frosted (works well as a key) acrylic tube, but I’d prefer at least some sort of fibre reinforcement in it for rigidity...and then I need that to have sufficient covering of resin that cutting the design into the CF doesn’t risk also cutting the reinforcement in the “inner” tube.

Might have to think of a different way of doing this...

What loads have the tube to take? If i should be structural in any way, a 80g glass reinforcement is as good as no reinforcement at all. No clear material comes near the propertys of carbon reinforced polymers.

What about an inner tube of thin fibreglass, then cast the clear resin section of the tube around the fibreglass tube, then bond that into the carbon tube?

Not an easy process at all for sure. That thin fibreglass is the tricky bit. If you can actually get it made at all, I'm not entirely sure it would work the way you want it to... 

If the tube inner and outer are carbon fibre then this will mostly take all or any loads, the inner clear part may not need any fibre reinforcing at all?

Why not set up two carbon tubes with the clearance you want, stand vertical , blank the bottom and fill from the top end with a clear casting resin?