I currently am only paying 40p per litre at the local Calor place by me, or 49.9 at shell if i can't get into Calor...
where's that Calor place mate?
I use Flogas at Castle Vale, which was 41.9 last time i went, or Birmingham autogas at Starcity, which was also 41p ish last time...
www.Petrolprices.com is useful for prices of all fuels. Not that it has every station/depot, but it's useful when travelling!
My local petrol stations charge about 49.9 (shell and texaco). I was gutted when travelling to wales and had to pay 54.9!!
Last time I went to Dorset though, the texaco in Shaftesbury was over 60p

(just checked, it's 62.9!)
I think the difference is based on supply/demand and how close a depot is to you rather than a fuel station.
If I go to london there's a cheap asda off the m40 near high wickham. wouldn't have found it without petrolprices.com. Now I've got a lpg atlas too, its useful for finding off the main route suppliers!
There are other websites listing lpg stuff like
http://www.drivelpg.co.uk or
http://www.lpgmap.co.uk/Plus you can get tomtom poi info for calor, autogas etc etc too.
PS according to that website the nearest Shell to Pontefact is at Castleford (Riverside), chargin 51.9p, but it's a bit off the a1.