Swede, you are breaking the law if fitting LPG without registration.
http://www.hse.gov.uk/pubns/indg387.pdf
http://www.drivelpg.co.uk/advice-and-information/faqs/
It invalidates the insurance and puts the driver at risk. I have found your details and forwarded them to relevant authorities, informing them you are fitting LPG, so hopefully you will soon be legal. Presuming youreach required standards of course.
Both threads pertaining to your work have also been forwarded to help them decide best course of action.
Clearly, if you are as good as your claims and are operating legally,this won't be a problem, merely affirmation.