From January 1st 2007 all foil insulations sold in the UK have to comply with BR443.

The following files are in PDF format.  You need Adobe Acrobat Reader to read these files.  If you do not have the Reader, you can download it free from here. 

L1A - Conservation of Fuel and Power in New Dwellings

L1B - Conservation of Fuel and Power in Existing Dwellings

L2A - Conservation of Fuel and Power in New Buildings other than Dwellings 

L2B - Conservation of Fuel and Power in Existing Buildings other than Dwellings 

BR443 - Conventions for U-Value Calculations (2006 Edition)