This is to avoid the harassment by the BBC licence fee agents of people who don't want to watch the BBC. It will give them proof that they aren't watching BBC programs. It's particularly important for the over 75s who will see the licence fee reintroduced next June and want to opt out.
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At present people are deemed to need a licence for the BBC if they have the means to watch it. This gives the BBC's agents the right to prosecute anyone with access to platforms such as Sky, Freeview, the internet etc for non payment of the licence fee. People have no means of proving that they don't watch the BBC at present which is grossly unfair. This is a particularly onerous burden and worry on the elderly.