If there is any legislation, it is legislation I feel comfortable ignoring. I have always carried mine in the boot, well strapped or chocked and empty of fuel which is in a separate 5l container.
Untill 2004 First Mate and I ran a Motorcycle business.
We had various vehicles for transporting new, used, crashed and our personal competition bikes.
Our trade insurer was well aware of what we did, the local Fire Brigade had lots of bikers who were in out of the shop and were interested in what we we doing, ditto local plod.
Unless legislation has changed, and I dont believe it has, carrying petrol and petrol engined vehicles is fine, up to the permissible quantities of petrol.
Even if it had not, such legislation would be aimed at commercial operations, not pleasure and leisure.
On the other hand, I have first hand experience of hazardous gases carried in vehicles without a separate closed compartment for the driver.
Before I retired, and after the motorbike shop I had a part time job in Bio-Science. The company would ship on dry ice-CO2 at minus 80 degrees C.
Our H&S would not allow the carriage of this unless the vehicle had a separate drivers compartment. We sometimes refused to load small vans without this feature.
As some will no doubt remember, some years ago three workers went into a refrigerated store on a ship in a British port and two died when they were overcome by lack of air-the CO2 had melted back to its gaseous form and displaced the breathable air upwards.
This is sensible.
In over 50 years of involvment with transporting petrol fueled vehicles I have never had a problem. I have had them catch fire-but never in the truck or van.
First Mate had two fires with her Vintage Racing sidecar outfit at Kirkistown in Northern Ireland in 1978.
It was running on Methanol fuel and it was a sunny day. You cant see the flames. Her passenger noticed the spark plug caps melting as she was warming it up.
That gave the game away...................................