I live in fairly central London, but wouldn't bother keeping a boat around here personally - I think there's very limited opportunities to really use it.
I guess it depends what part of London you might move to, as that makes a big difference to the drive. I live/work at Canary Wharf during the week, but family home and my boats are down in Poole, so I need to cross right through London to go home, which makes it a 2.5-3 hour journey. If I lived in West London, would cut an hour off, but make my daily commute nasty!
I do a lot of voluntary work with Sea Cadets over on the East Coast - that's a very easy run out of (Central/East) London along the A12 after the traffic dies down in the evening.
Or similar to WhiteShark, Portsmouth/Chichester are pretty easy to get to for Solent access, if you live Central/South London.
Or
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