Unless it’s a HGV there’s no general restriction on parking a vehicle on a road, even if you can see it and don’t think it’s pretty. That’s kinda what roads are for you see, vehicles.
If it’s dangerous to park next to it, don’t park next to it.
What you might have some luck with though is this:
we live in a Victorian terrace where the road is wide enough for one parked car and one moving car…..
They can’t legally park in a manner which would stop emergency vehicles getting past. Can you get a fire engine down that space, do you reckon?
Does it have valid road tax?
Unlikely, there’s no such thing as road tax.