Visited Costco Thurrock / Lakeside and noticed that fuel now available (some other branches have fuel already and there appears to be plan to extend to others).
Diesel (104.9p) was 4p cheaper than best local alternative of Tesco Lakeside (108.9p) according to petrolprices.com latest update.
As usually case with Costco, members only deal, but saving on full tank for me is ~£2.50 so I will get most of my yearly membership cost back by filling up when I visit to buy other items.
Appears to be fully automated and debit rather than credit card after first scan membership card.
Handy for M25 / A13 traffic if you are unfortunate enough to have to commute in this area.