Well to be exact its probably not "illegal" if its a picture of a vehicle in China. Its probably not illegal in most of the world, but if you look at the legal requirments in the Webasto manual you will see that it is illegal in Germany and that the relevent reguations apprear to be EU ones which means that they "could" apply in the UK. In Germany where they operate type approval it would also be an offense to install the heater yourself. The UK has (in my view very sensibly) opted out of type approval. But there remain the "contruction and use" regs. When I did my own biofuel conversion I ran into the UK regs regarding the location of the 2nd tank and the fuel pipe routing, my insurers required the installation to be inspected. Its was most definately not permitted to run the fuel line inside the passenger compartment. If I read that photo right then both the tank and fuel line are inside. My worry is not the illigality or otherwise, the law is there to protect people, often from themselves. I used to work with a boss who had been the lead investigator for carbon monoxide deaths in the UK. He impressed on me what a harrowing job it was and how unecessary the deaths were. What affected him the most was that they were usually young and poor and they had ether done the installation themsleves or it had been done illegally by a dodgy landlord. In all cases the savings over doing it safely were minimal.