There is a uk section of this forum with a number of guys running jb4 (myself included).
Juiceduptuning.co.uk is a UK distributor for the jb4 and numerous other products, checkout the website.
You just need to work out whether you have an N54 (twin turbo) or N55 engine (twin power turbo) - 2009 was the year it changed...
Car: 2010 Jaguar XFR (Stock - For now)
Gone but not forgotten: Highly Modified E90 335i LCI M Sport Manual (circa 480BHP/500lb ft)