It’s no longer in production bike is it?
The difference I’d assume is purely spec, the frame will (should) be the same through the ranges.
As I can’t find them online, other than old reviews, I’d guess that the 1.0/2.0/3.0/XS1/XS2 are just spec level from different years. The level goes along the lines of 1.0 being highest/most expensive in the range and 3.0 being lowest and cheapest to buy (of that range)
Sorry can’t help you more
(more than you got originally, expecting responses at 1am in the morning on a UK specific site ain’t gunna happen)