If you need proof of exemption for the 15th ,I can't see how that is enough time for a Doctor to give you a letter. In any case, from lockdownsceptics "The Government must know that facemasks are useless, so why this ridiculous assault on our liberty? The only explanation I can think of is that ministers like Grant Shapps don’t think the public will believe them if they tell the truth – that it’s perfectly safe to use public transport – because they’ve succeeded in scaring the bejesus out of them over the past 12 weeks. The only way to coax the labour force out from under their beds and back into the workplace is to make mask-wearing compulsory."