Estuary English [1] -- the English spoken around the Thames estuary. It has, arguably, been the "standard" non-posh British dialect for a while.

As a North American, I find it one of the harder accents to understand. It has undergone a lot of interesting sound changes in recent decades, not shared by many other dialects. Likely a result of dialect flattening from 20th century population movements. "Football" -> [ˈfʊʔbɔo] (sounds like "fuh-baoh" to me) or "bottle" -> ['bɒʔo] {"bah-oh"?) or "Tuesday" -> [tʃuːz.deɪ] ("choose day").

[1] https://en.wikipedia.org/wiki/Estuary_English