It's fitted to a Howard Gem, I think I got to the bottom of it now, after stripping the injector down, everything looked all nice and shiny so I reassembled it and tried again, frustratingly still no action from the end of the injector, then after many turns of the handle I noticed a slight weep around the outlet of the pump, so I stripped the banjo Union off cleaned all the matting surfaces then tightened it all back up again and hey presto, a fine mist of diesel from the injector
Hopefully it'll still work when under compression in the cylinder, but I think I might need a starter fuse for it now, fingers crossed I'll get it going soon,
Thanks for the advice so far guys