The European version of the app from https://www.mylpg.eu/lpg-prices-across-europe now includes UK (so not sure if Dave has been sharing info or if they've nicked it) but that will allow you to put a route in and show stations on the route. Covers all of Europe (if you need it). There's an Android app on the Playstore (look for EU LPG) as well as Garmin and Tomtom POI files.
Their info is a combination of info from all over the place - Hence why when you look at it, its full of duplicates, inaccurate locations, stations that don't exist, stations that never existed in the first place and out of date info. Its possible to get duplicates and closed stations removed from it by contacting the admin on every instance. I suspect the European info is somewhat better than what the UK info on there is.
Some of it appeared to me to have been found from the nearly defunct printed map book - http://www.go-autogas.com/ if you don't know the one I mean, and that was the original reason for Richard starting Filllpg - as the info on their supposedly superior POI files that you got with the map was so poor, with stations shown not merely in the wrong place, but frequently not even in the right county or even in the middle of the sea. Though its equally possible the info went from myLPG.eu to them rather than the other way round.
TBH though, with the amount of stations that seem to be disappearing (Shell seem to be culling a load of theirs now) you'd be better with an app that downloads updates regularly unless you want to update the satnav regularly as well.