It might be worth a look to find a Netgear reseller in the US willing to sell to the UK. Diskless units are around ~$650 or so if you look, so it would cut it down to £325. Not sure what your price range is though. For me, the price was justified when they bumped the warranties up to 5 years.

Whatever you pick, make sure to find some actual reviews on the units, since specs don't say how well the device will actually run, and bargain basement prices on a box might be a sign of a really old and slow model being sold still.