For the British accent, just stream the BBC World Service.
It is mostly impeccable English, and as they know it's for a global audience they tend to narrate/speak a little more slowly.
[Aside: I remember in the Amazon after weeks out there, in our basha, with a with a British Army Clansman radio for which we got the aerial right up a tree (via crossbow), and we managed to tune into the BBC World Service.
Never has a programme on Medieval wind instruments been so utterly riveting (The next progamme was on distinctions between breeds of pedigree show dogs! lol), the accent alone almost brought tears to my eyes
]