by the letter of the law that is true. However, under animal welfare law, which they can and will apply as needed, a 410 would be classed as unsuitable weapon and you could be done for causeing undue suffering to a creature. 12 bore and minimum of 32g of No.5. Walked up hare are invariably running away, so you need to shoot/carry a gun and load that would be up to the task if need be.
Although I'm not a shooting man ,,, and I stand to be corrected,,, but I wouldnt have thought there was a law saying you can't shoot a hare with a 410,,,, of course it's not the prefred weapon,,,but surly no law