Thanks for the input. It's ok now but of a bit of a struggle. Just to conclude the thread for the odd few on the 350z site like me who are daft enough to like getting their hands dirty....
I tried the technique I saw on YouTube where you pump fluid up from the slave nipple with a clean pump oil can and let the bubbles all come up with gravity. I did this twice, clearing all the bubbles but each time the clutch pedal just flopped down so I went to plan B.
Halfrawds had a Gunson automatic system (about £17) with a bottle you put next to the fluid reservoir and then use compressed air from a spare tyre to pump the fluid through, genius!
However, none of the various caps they supply for the reservoir fit a Nissan so you have to drill a 10mm hole in the cap to take the link tube from the bottle. No problem just blank it off afterwards.
One essential thing. Tie the reservoir lid on firmly, as with 20 psi pressure it blows clean off and showers you with hydraulic fluid, not good.
Anyway I ran this system through a couple of times, having some difficulty with the bleed screw, too loose and it leaks around its thread, too tight and the flow is restricted. I ended up twiddling that under the car and leaving everything else to look after itself.
This all seemed to go ok until I tested the pedal and it flopped to the floor again.
I was getting a bit exasperated. The line was still on the bleeder and no air had got back in so I pumped the pedal by hand with the bleed open and air was coming out. Once clear I ran the pressure system through again and this time everything seems fine.
I think for the first time since I got the car in Feb it is not leaking oil (from rusty sump) or hydraulic fluid (from rusty flex pipe). Flippin hooray!