Aviation fuel is cheaper in the US. For example, a US Gal may cost $2.40 which equates to 63c per litre or 34p at todays xrate. I normally pay around 80p a litre here, so fuel in a 10gph Cessna in the UK will cost £30.40/hr and in the states £12.92/hr.
There is a difference of roughly £60/hr between say an 8gph Warrior II here and the USA, of which the fuel costs £13.98 more per hour in the UK, which still leaves a gap of £46.02 between the UK and US.
I can only assume that the higher ownsership costs can be attributed to higher maintenance costs (CofA every 3 years, as opposed to never), higher initial purchase costs - though I don't know why anyone would allow themselves to be ripped off by buying a more expensive aircraft in the UK when they can go to the states and buy one cheaper. Import duty on an aircraft is 0% though you must still pay VAT.
I can't believe that cost of living between the UK and say California has much to do with it. As an example, buy a house in Cali, a reasonable area and you're looking upwards of $400,000. Car insurance is not cheap, medical insurance, super market prices are comparable the only cheaper thing is fuel.
Maybe it is just a classic case of "rip-off-britain".....
EA