Yes agree with all that Gra

Back in the day (early 2000s) I had a Ford Scorpio Ultima 2.9 which I converted to LPG

This was when it was about 30p/litre. Did over 100k over about 7 years. Armchair comfort for small car economy

Oil changes were as clean as it went in

No incentives to do it now. Only a few filling stations left and it now at about 69p/litre

But I wish I’d kept the Scorpio. The buyer drove it to Scotland and absolutely loved it
yeh, I had a top line Scorpio too .... lovely motor .... and yes HMG paid token lip service to the promotion of LPG at great prices and then shat on everyone. If they'd been serious about it there wouldn't have been so many obstacles put in the path of its wider adoption !!
I think you two are both barking up the wrong tree here. Leccy and hybrids pay nill road tax as they are greener/less polluting and helps the govt towards meeting their own targets so in a way its not nil tax but govt subsidised. You didn't convert to lpg to save the planet you did it because you were running ancient tech gas guzzlers you couldn't pour juice in fast enough with a bucket and were looking for cheap fuel.
so was LPG Gaz .... 'swhy LPG FLTs were able to be used indoors and in food processing plants ... could breathe around them
if hybrids are nil VED anything running LPG should've been the same .. but wasn't without huge hoops to jump through ..
LPG converted vehicles are essentially hybrids too, 'cept they spend the largest proportion of their time on the greener fuel, unlike the paltry 30 miles the leccy hybrid can.
as for gas guzzlers .. yeh people converted them for the comfort, etc. they gave, running at 'fiesta' type running costs. Could equally run a 'fiesta' on LPG and have the running costs of a roller skate .. why bother though?
Most conversions were far from ancient though Gaz ... my P38 was done at 6 mths old and a lot of manufacturers (Ford, Vauxhaul, etc.) were, or starting to, offer it from factory ... and then HMG dumped on the industry and it got abandoned ..... interestingly, Daewoo have just started offering factory LPG fits for their Dusters

.. and on small capacity motors.
The calorific value of LPG is much higher than conventional petrol / diesel fuels, massively cleaner burning and a lot more efficient.
It's also a by-product which the refineries were having to pay a levy against to burn off excesses, ...or dispose of it elsewhere.
Spain / Portugal were big adopters and the oil co.s were shipping it out there by the tanker boat load at a penny a litre or less, when the home market was getting charged 35p/ltr. If HMG had been serious about promoting its adoption, the home market would've consumed all they could've produced, instead of wallowing in uncertainty about HMG's attitudes towards the whole thing

in 2001/2, I was selling 6000+ litres a week and was one of four outlets within 5-6 mile radius ... it was circa 25p/ltr ....