Neither has the correct figure although I think it's a typo in Courtman's case.
You can drawback the full duty which is 27.34 pence per litre - thankfully it hasn't gone up for a few years.
http://www.hmce.gov.uk/business/othe.../roadfuels.htm
Simply fill out a drawback form (HO60 I think), send in to Newcastle, then a few weeks later a cheque for the duty appears. Simple.