Craftex sell a fire retardent chemical for carpets and upholstery. The only issue, is that they wont supply any sort of certificate to give to customer to confirm the chemical make-up or that the application was done correctly.Understandibly.
Having spoken to Craftex on this issue, they suggest that you create your own certificate, or something similair, letter headed with company logo to confirm you have applied the chemical in accordance with manufacturers instructions and that the chemical conforms with blah, blah, blah.
I would then suggest you speak with your local fire station officer, who would normally do the fire check at the premises to see if what you intend to do is sufficient with him.
I know it all sounds a bit dodgy but the chemical isn't that expensive for you to buy and you could do a hell of a mark up for your efforts....
Cheers, Daz Roberts