How many miles to the litre?

I remember feeling great pleasure when the British government decided in 1965 to go metric. I had resisted all attempts at school to make me learn how many rods or perches there were to a furlong or how many troy carats in an avoirdupois scruple, and I was proud to be one of the few Brits who knew their height and weight in metres and kilos.

Yet here we are 45 years later still muddling along with a mixture of systems. The height of absurdity is the fact that we meaure petrol in litres and distance in miles. Whether you want to know your vehicle's performance in miles per gallon or litres per hundred kilometres, you have a head-cracking calculation to go through.

Our failure to carry metrication through is perhaps another mark of the growing American influence of America, where they crashed a probe on Mars because one team measured its altitude in feet while another calculated its speed in metres per second. Yet the Americans don't strictly use Imperial units, since they have their own pints and gallons. And how shall we ever replace knots by metric speeds with hundreds of airlines working in knots and feet? What a mess!