Not really spur of the moment. There had been planning & Sheila was going back to London soon. So not much choice.
He had been ranting about it for months with no action according to Julie, then carried it out out of the blue. Julie says she didn't think he was being serious.
Very much if what Julie says is true a rash decision " his I've been thinking on the tractor, it has to be tonight " points to that.
Julie's WS also points to periods where he never mentioned talking about it.