The one bike you linked to is not a very fair test because this is one of the earliest know Colnagos in existance. Kind of like comparing the prototype of the aforementioned Ferrari to a production Rover.
That said, part of what you describe may be proximity since there would clearly be lots of Hetchins and Holdworths lying about in folk's sheds around the UK but not as much for the Italian marques. Another BIG factor in the price of Colnagos is that Asian buyers love Italian bicycles and they have been driving the price up lately.
BTW the rare handmade English bikes are very expensive here in the US, as an example look at the Claud Butler sold by this same seller:http://www.ebay.com/itm/Rare-Vintage-Ci ... 7675.l2557
I was old school before it was cool