Location	Postcode	Franchise	Grade	Price/litre	Date	Website
Morrisons A386 Tavistock	PL19 9DG	Morrisons	E5 (99) & E10 (95)	160.9p	24 Feb 23	---
Sourton Cross A386 Okehampton	EX20 4LY	Shell	V-power unleaded (99)	151.9p 159.9p	1 Sep 21 4 Nov 21	Click Link
Whiddon Down off A30	---	"Synergy"	E5 & E10 regular only	---	14 Sep 21	---
A30 East of Okehampton	---	BP	E5, E10 regular & DERV	---	14 Sep 21	---
Tesco Seaward Way Minehead	---	Tesco	E5 Premium	---	14 Sep 21	---
Trerulefoot Roundabout A38	PL12 8BL	Shell	V-power unleaded (99)	156.9p	13 Oct 21	Click Link
Tesco Axminster	---	Tesco	---	---	5 Nov 21	---
Co-op Bovey Tracey A382	TQ13 9DX	Co-op	97 octane unleaded	157.9	23 Nov 21	---
Texaco Yelverton A386	PL20 6DT	Texaco	E5, Regular & DERV	153.9 151.9 165.9	16 Dec 21 17 Dec 21 4 Jan 23	0700-2000 hrs

So far, I have had little feedback, and only Shell have made an attempt to help us find E5 petrol:

Shell has an useful web site HERE from which I may extract some data in due course. You have to wade
through some cookie blurb, but it is worth a look. If I find anything similar for other suppliers elsewhere
on the net, I'll post another update. (NB the Shell site needs an up-to-date browser to make its clever map
work, so if it does not display an UK map in a few seconds, update your browser and try again.)

South Brent A38	TQ10 9ER	Shell	Website	---	---
Pear Tree Self Serve Newton Abbot	TQ13 7RB	Shell	Website			Not 24h
Torquay Riviera Way	TQ2 7AR	Shell	Website
376-384 Torquay Road Paignton	TQ3 2DN	Shell	Website			Not 24h
Trago Mills	TQ12 6JD	Shell	Closed until 30 Sep 21			Not 24h
Exeter Road Crediton	EX17 3BN	Shell	Website
Cullompton M5 Jct 28	EX15 1NS	Shell	Website
Kingsley Village Penhale	TR9 6NA	Shell	Website
A30 Carland Cross Newquay	TR8 5AY	Shell	Website

BP has this site, which is not quite as informative as the Shell one.
Another possibly useful site is petrolmap.co.uk, if you are prepared to sign up, giving them your postcode,
car registration mark and a cellphone number.