UK Fuel tax rates are here:
http://www.hmrc.gov.uk/budget2011/tiin6330.pdf Then add VAT.
So my maths (Provider = distribution, refining, maintenance, etc):
if the AVGAS price is £2.10 per litre, that means that each litre consists of:
Duty: 37.7p (18% of total)
Provider: £1.373 (65% of total)
VAT (20%): 35p (16% of total)
so HMRC gets 73p per litre.
Comparing to Unleaded petrol at the BBC's £1.34 per litre:
Duty: 58p (43% of total)
Provider: 54p (40% of total)
VAT (20%): 22p (17% of total)
HMRC gets 80p per litre
Actually not that much in it.