Oxeagle's right, duty will stuff you. Even without duty, shipping and handling costs must be uneconomic, otherwise all our Avgas 100LL here would be imported from the US. (Take it from me it isnt
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Anyway, its possible to get fuel even cheaper over here. Just find an aircraft that is approved for Mogas, and fly it on a return trip with full tanks to either Channel Islands/IOM/Ireland/France. The nice Mr Brown will happily hand over 47p/litre drawback, making your fuel cost around 41p/litre (at todays prices) if you use it all, considerably less if you dont
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