Another storage option is Car Vault, the Bike Shed has a deal with them if you’re a member.
It’s not as convenient as you’re own garage as it’s not open 24/7 but it’s a central location.
https://www.carvaultlondon.co.uk/services-tariff/
A couple of members here are using them.
I’ve heard some people keep their out of London address for the insurance…