TWR
I don't think you'll find the law has changed and my comments aren't particular to vehicles with flammable goods.
Here's what the Government has to say about getting an HGV Operators Licence:
WHAT IS MEANT BY AN “OPERATING CENTRE”?
4.1 An operating centre is where your vehicles are normally kept when not in use. The operating centre should provide sufficient off street parking for all your vehicles and trailers.
WHAT CONSTRAINTS ARE THERE IN ACCEPTING A SITE AS AN OPERATING CENTRE?
4.2 When you apply for a licence, you will be asked to list your proposed operating centres, with information about the vehicles which are to be kept there. The Traffic Commissioner will need to be satisfied that your operating centres are suitable - for example, that they will be big enough, with safe access, and in an environmentally acceptable location. If you do not own the operating centre you may be asked to provide evidence that you are entitled to use it.
All I'm saying is that if an HGV is consistently and persistently being parked in a residential area, it isn't being operated in accordance with its operating licence and if the Traffic Commissioner was approached, you might get something done to stop it.