Just so we are not comparing apples and oranges and as further food for thought

UK =                $ 5.48 US / US gal (86% Taxes = $ .77 per gal after taxes)
NZ =                $ 2.85 US / US gal
Australia =         $ 2.38 US /US gal
Canada =          $ 2.40 US /US gal (approx 40-50% Taxes = $ 1.20 per gal after taxes)*
United States =    $ 1.75 US /US gal (approx 30-40% Taxes = $ 1.05 per gal after taxes)*

*calculated at the highest amount

Until it is determined how much per gallon is actually taxes in each country, my question would be why does the UK pay so little for a gallon of gas?

One possible reason is that it costs more to transport oil via pipeline than it does to ship oil by tanker. Contrary to what was stated previously, from figures I have seen, Canada is the largest supplier of petroleum to the US (not Venezuela) unless the US considers petroleum fom Canada as their own. Petroleum in Canada (except for the east coast) and from Canada to other areas of North America is primarily transported by pipeline and as such costs more.

some Canadian statistics

some US statistics