If you're going to keep the bike in London, then the first thing that you may want to consider is the cost / benefits of secure parking.
Sometimes it'll make no difference to the overall cost of your insurance premium, but I would guess that it 'could' equate to an (ovarall) saving to the costs, if a bike is locked away in a secure garage.
The trick with on-street parking is to make your bike look less inviting to any would-be interested parties... Therefore, something that's not all that shiny or attractive can be a bonus.