Right I worked on this a bit more today and got a bit farther but it still won't fire
I managed to eventually get the spark plugs out, they where in really tight...
I then put a new battery on (640 amps) and fitted a new plug onto an ht lead and tried to fire it to see if I got a spark. I didn't
So I tried connecting various other bits of the loom and eventually found that for some reason the fan switch has to be connected to get a spark?
So with the spark plugs removed, I put a bit of oil down each plug hole (maybe a couple of tablespoons worth in each plug). I then turned it on to help work the oil into the pistons and it spins round nice and fast.
Next I put all the new plugs in properly and connected the HT leads. I then tried to start it again and now it doesn't even spin at all. You can hear the starter motor struggling trying to spin the flywheel but nothing.
Any ideas what to do next??