Thanks for that tip MarkyB, it does feel pretty savage when this problem happens no "warning" burps or coughs, like I said it happened on a downhill stretch and I tried to "bump" start while still rolling and got a couple of small coughs but no dice, 2 turns of the key and going fine again!
Our moggy began cutting out on the motorway for second bursts on friday (this happened once before, but not as badly). Finally got a lift home on a pick up. The annoying thing was up to fifty everything was fine, then bang! Guy on the pick up truck drove it onto the back of his ramps no worries, got in the cab and said the coil was breaking up under the heat of high speed. I can believe this, as the coil was apparently leaking its oil slowly from the rim. Theory, as he explained, was as the coild heated the areas without oil are not kept cool and expand and break. As the coil cools the wires reunite and it starts working again. I was scpetical, but a new coild has (hopefull) fixed the problem as we've been back on the motorway without issue. Wouldn't have minded, but the coild was only two months old!
My 'never' rule with coils doesn't apply to new coils - especially if they are designed to run on ballast ignition - and are fed 14 volts instead! I don't agree with his 'break'/'remake' suggestion - but it could start to short internally if low on oil. A coil leaking oil should always be replaced.... have you any idea how hot the coil used to run? My car - the coil is mounted vertically away from the engine - and is no more than slightly warm immediately after a run.