The stuff I used was made in a factory unit on the estate where I work. It was initially produced for that company's own vehicles but offered for sale at a heavy discount over standard diesel to people working on the estate.
Initially made from WVO but later from SVO (Rapeseed oil) when WVO supplies became problematic for the volumes required - around 1,000 litres per week.
Eventually became too expensive for them to sell and they only use it themselves now.