Bit different to having one in your own van as a sole operator to having them with employees in.
Im perfectly happy to risk my own life as im confident the way mine is secured is sufficent but i wouldnt want the worry of it killing an employee and me being liable.
Wonder if the Modded owner chap from teeside window cleaning got done for it
Well scouting round the interweb it seems the other vans were served prohibition notices for the way the tanks were put in.
If the accident is as has been suggested/described it looks like a Citroen pulled out and the Van hit but slewed off into a field. To me that would indicate that the van didn't come to an abrupt halt; but IF it turned over or hit something else to stop it abruptly and the tank wasn't strapped/bolted down properly and/or IF there was no bulkhead then it MIGHT have broken free and smashed into the cab area.
A lot of conjecture.
I would be happy to self install (as in get a frame made up by a welder/blacksmith with bolt holes and correct plates for the underside).
Now a question is asked of GrassRootsMotorsports Magazine here about self installing an antiroll bar into your car for motorsports and here are the instructions.
https://grassrootsmotorsports.com/articles/how-install-bolt-roll-bar/#:~:text=Roll%20bars%20can%20be%20welded,of%20removal%20in%20the%20future.
So to me if a competent D-i-Y'er is allowed to arrange for such in a competition I see no difference in principle to installing a tank.
I accept different insurers choose different criteria and I hope that the incident in the north-east, while tragic doesn't stop a conscientious business owner arranging for his own tanks to be installed.