There's a problem with the Halfords site at the minute with every page coming up not found, but looking on the Laser Tools site (I think it was one of their products from the Halfords link) it has a maximum of 235mm so no better than the Screwfix option on that count.
Laser Tools - http://www.lasertools.co.uk/item.aspx?item=1480
Most of the compressors are in the region of 220-250mm, until you get into the professional category, for example this Sealey one opens up to 356mm (their cheaper ones are listed as 230mm)
Sorry though, I can't help with what size you'd need for a Clio, although I'd expect the Halfords / Screwfix etc ones would suffice - they're probably classed as professional so far as Haynes are concerned, they probably mean use a proper tool rather than bodge something together.
