Its says free shipping in the US and UK, so I'm guessing, as Canonical is based in London, they'll do the importing and deal with duty, so the price you see is the price you pay! I'm guessing.
Good question. No idea! If I get charged the VAT and duty, I think I might be able to make up the £90 by charging the other geeks in my office a "fondle fee".
We're all forced to use windows, I might even be able to make a profit :-)
A quick google suggests you could be liable for around £90 in duty & VAT[1]
[1]http://www.dutycalculator.com/popular-import-items/import-du...