Got our Crit Air with a scan of the V5.
The Euro X rating is a function of the year of first registration - with some caveats on Euro 6.

The RAC has a table. Pretty sure I put our Feb 2014 car down as Euro 5.

Paul
Costock, UK
Plus Four 75th - Furka Rouge - Pip
Disco 5
Teddy - 17h1 Irish Draught cross