isn't this where i came in?
You tried another battery, made no difference... so can't see the point in buying one.
You've removed and cleaned all battery cable and earth connections so don't really see you getting a voltage drop at any of them.
You've eliminated the ignition switch as far as cranking goes by connecting lucar direct to battery.
So the only thing is, as ianda12 rightly pointed out, the starter test on the floor does not put the motor under load which is why I was trying to establish how powerful it seemed. Anyone who has done it before would know they accelerate with a fair kick which is why I said keep your foot on it to hold it steady. You say it spun 'quite quickly' which doesn't sound like it's zapping round like it should so is making me doubt the condition of the motor rather than the usual solenoid fault.