Hi again,
Well good news, Rob did something to it (well a few things) and its been starting everytime for the last two days! It had been playing up for months so he's pretty excited about it.
NOw, what did he do I hear you ask,
(and even if you didn't I'm going to tell you anyway)
He wriggled the ignitions wires (very technical)
He tightened up the elbow thingy where the gas goes into the carburettor (it was loose apparently)
Cleaned connections and tightened wires in some little black box thingy
Cleaned the wires and solenoid with some sandpaper

Which was the magic cure???? stuffed if I know, coz he didn't test it between each thing

Thankyou to those whose replied