And yet everyone speaks in their own dialects, pronunciation, many places have their own twists on grammar etc (RP is an accent, so grammar isn't relevant when discussing RP). Let me quote myself from my original answer:
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"Standardising a language" never works. Prescriptivism rarely does because languages are living things and evolve no matter how many rules you throw at them.
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So, Britain has standardised English. Did it work? Well, not really, almost everyone keeps speaking in their own way. As for government speeches... Here's SNP's Ian Blackford in the House of Commons (not government, but still, a high-ranking politician) [1]. And I believe Americans, Australians and New Zealanders have no problem understanding their politicians despite English not being standardised.
As for TV. Have you ever watched British TV outside BBC News programs (which traditionally, but not necessarily use a "BBC accent" which also changes with time)? Just a few samples: Big Narstie Show [2], Eastenders [3], and, yes, BBC News (around 10:02 mark, 16:30) [4] Or even something like this [5], but this is an extreme example.
All that despite English having been standardised for more than a century.
