Along a sun-dappled canal towpath in picturesque Hertfordshire countryside, a grey-brown bob rises and falls with the effortless bounce of a lithe, spectacled figure gliding her way past dog-walkers and afternoon ramblers.
There is a watch – one of those smart-technology devices capable of producing all sorts of unnecessary metrics – on Sarah Roberts’s wrist, but she has forgotten to switch it on. Roberts, a grandmother of five, tends not to take note of such things.
