A little trick that I find useful is to remove the brake lever and use a drift directly on the master cylinder piston (instead of the lever) - works a treat.

Get a DOUBLE BANJO BOLT BLEED NIPPLE, replace the banjo bolt on the master cylinder with it and never have problems again.
Bleed the callipers as normal, bleed the top banjo bolt, done.

regards
jon

Cheers lads for all your suggestions and support got loads of things to try now. Spot on advice!