Here are the great list of bitcoin events around world:
https://www.coindesk.com/bitcoin-events/

You can find events exactly in London:

September 20, 2017   Blockchain Live: Unlocking the Value of Blockchain for Enterprise and the Public Sector
September 24, 2017   The Dash Conference
September 25-26, 2017   World Blockchain Forum - Investments & ICOs
October 5, 2017   Blockchain Summit London
October 11, 2017   ICO Event London
October 12, 2017   TRUST Megatrends, A Blockchain Masterclass
October 13, 2017   Healthcare: Unblocked
October 31, 2017   Marketforce's 3rd annual The Blockchain Summit
November 14, 2017   Digital Commodities Summit
November 21-22, 2017   Fintech World Forum 2017
November 28, 2017   Blockchain Summit
February 13-16, 2018   Finovate Europe 2018