Pity those sorts of things dont come up on ebay UK very often. I'd love to get my hands on a diesel engine like that to make a generator, or maybe convert my tractor from petrol to diesel.
I have a one-click ebay 'Yanmar' search in my Mozilla toolbar. Quite often, it brings up Yanmar-engined generator sets. I see that a search on ebay-UK gives similar results, so you might be able to buy one cheaper than assembling it.
I'd like something in the 10kw range for welding.
I wouldn't be surprised if the genset with the BIN price on the link you gave was stolen, its way too cheap.
£20.00 was what he set as an opening bid, but no one bid before he ended the auction prematurely. His secret Reserve (minimum he would sell for) was probably higher.