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I had this the other night and didn't like it much. Too metallic tasting for my liking, which I have been led to believe is down to excess carbonation, but I'm not so sure.

I've always assumed that metallic thing to be an English hops issue, as I generally only meet it in English bitters. Haven't tried this one yet, though.

I have wondered about the metallic tast. I think carbondioxide certainly contributes but there is something more to it. Hops are certainly a likely cause because as you said, English ales tend to have this character. Sadly this flavour in excess is enough to ruin a beer for me.

According to "How to Brew"

Metallic
Metallic flavors are usually caused by unprotected metals dissolving into the wort but can also be caused by the hydrolysis of lipids in poorly stored malts. Iron and aluminum can cause metallic flavors leaching into the wort during the boil. The small amount could be considered to be nutritional if it weren't for the bad taste.

To my mind metallic is pretty common among English ales. The CO2 idea came from Brewlab where they said that people who complained about the metallic taste from canned beer were not tasting the can at all, merely the slightly higher CO2 levels.

It does seem like something more fundamental like the water or malt. But why would you brew with water you knew to be high in minerals? Maybe the locals got used to the taste and it spread from there.

Is probably more suited to home brewing where they just use the water they have.

CO2 seam the most likely culprit