Telegraph: Long ago, in a different life, I was a milkman for the Co-operative Dairy. It meant getting up very early and as we loaded our floats, my older colleagues would recall chasing bad-tempered ponies over the South Downs in the dark to harness to their floats. Fortunately for me, my Smiths Cabac milk float had a lead-acid heart that didn’t require sugar lumps to persuade it to work. The 48-volt battery pack would propel my float at 20mph across the Newhaven Marshes and then, six hours and maybe …