 YOUR Energy and Environment pages have carried several articles regarding future transport energy, many of them influenced by Professor David Mac-Kay's book, Sustainable Energy - Without the Hot air. In it he makes the claim that electric vehicles are up to five times more energy efficient than fossilfuelled cars. This claim is not based on similar vehicles and does not allow for generating losses at power stations. Professor MacKay has apologised for any misunderstanding his statement may have caused.  For mixed driving conditions, a modern turbo diesel will always be more efficient than a similarsized electric car whose energy comes from fossilfuelled power stations, because there are fewer losses involved. Electric vehicles are only cheaper to run because the government has not got round to taxing transport electricity - yet. If we compare ultimate efficiency, we find that the electric aptera does 190mpg equivalent while VW's diesel 1-litre car does 280mpg. The Volkswagen will also have greater range and enough "waste" heat to power a cabin heater.  We need to face facts, not green dreams. Electric vehicles will only make any sense once we have converted to an all nuclear power generation system. In order to transfer to all-electric road transport, we will have to double the number of power stations in the UK. That is how much energy road transport uses.  Ralph Ellis Shrewsbury, Shropshire