So a quick check with the multimeter showed 12v @ coil with key on and 7.5v cranking. Checked the key and 12v main being fed but 7.5v at start terminal.

Great, new ignition barrel. Zipped over to the other B110 and pulled the other one out. Turned out to be fairly simple to do.

Back over to the problem B110, put the barrel in , wired it back up (changing a terminal that wasn't 100%) and .................... ................ ............bloody nothing bloody bloody.

Check with the multimeter shows 10.5v @ coil when cranking. Screwdriver in Coil lead has spark now jumping over 20mm to the strut bolt earth before it suddenly zapped the crap out of my hand. Spark seemed strong by touch . Still orange though. Pulled out No.2 plug and checked spark, a nice strong bluish.

Ignition barrel also showing 10.5v @ start position.

Incidentally, the 2 small black wired going to the dizzy from the module showed 1.2v with key on and around 1.3-1.5 with motor cranking whilst the 2 connected to the coil showed around 12v. I have no idea if this is normal or not...