Most of the organized crime bosses in England are still of White British descent ( most of them working class English, but also some of Irish descent such as the Adams).
Granted there are also some very big :
Turks and Kurds ( regarding the heroin trade )
Turkish Cypriots ( such as the Arifs, their activities can be compared to the ones of the English crime 'Firms')
Jamaicans ( the ones at the top of the Yardie gangs)
Nigerians ( the ones at the top of the Peckham Boys )
Black Brits ( the majority of the so called 'Black Brits' are of mixed race nowadays)
Chinese ( Triads are also active in the UK but mostly stick to their own community )
Vietnamese ( there are some big cannabis barons within their community)
Albanians ( they focus more on the vice trade )
Colombians ( their activities are mostly limited to the import of cocaine)
Somalis, Pakistanis, Tamils and Bengalis also have gangs with their top guys ( they mostly focus on the heroin trade )

I think the Maltese are done nowadays.
There are Russians active in the UK, but mostly for laundering money.
In general the days of the so-called 'stylish' and 'flashy' organized crime ,be it in America or the UK, are over. Gangs regardless of any ethnic origin are becoming more gritty, but just as powerful and just as dangerous.
In general the traditional white English crime firms will always be there and they will still be the biggest in England for a very long time, even with the emergence of more than a dozen other ethnic organized crime groups.
The most dangerous organized crime groups in the UK I've read about were still the English Firms such as the not so well-known but still notorious Canning Town Firm or other East End London firms, the South London firms or the Liverpudlian crime gangs.

PS : I'm not from the UK, but I did a lot of research on organized crime.