I've researched in London many times over the years, and in particular at:
- The National Archives in Kew http://www.nationalarchives.gov.uk/
- The Society of Genealogists in Central London http://www.nationalarchives.gov.uk/
- London Metropolitan Archives https://www.cityoflondon.gov.uk/things-to-do/london-metropolitan-archives/visitor-information/Pages/default.asp
- City of Westminster Archives Centre https://www.westminster.gov.uk/archives
- British Library https://www.bl.uk/#
- British Museum https://www.britishmuseum.org/
- Imperial War Museum https://www.iwm.org.uk/visits
Understanding the historical context of your ancestors lives adds much to your research. Understanding what was happening at the time, can help explain some unusual surnames, family movements to new cities, etc.
The National Archives at Kew is well worth the visit, and it's a lovely day out of Central London. In particular I have researched Royal Marine records there, and was lucky enough to have found my GG Grandfather's Royal Marine attestation from 1837 - which gave me his birthplace (a village I hadn't researched), and a physical description. It was amazing to be handed this piece of history to look through!
So get yourself registered for RootsTech London in October, and let the research begin!