Kept looking at it suspiciously in the garden, goading me it was. So I pumped up the (totally disintegrating) tyres, unseized the chain and am riding it in the sun on local journeys. Love it.
As I thought. I think the novelty of a bike that rides like a pogo-stick has worn off now, so I'm having the head-badge and good bits off and gifting the rest if anyone wants it?