How do people store bicycles in London?

In my experience, it seems fairly standard practice for the tenancy agreements supplied by agents to forbid the storage of bikes in properties. I have always just done so regardless, though I can understand why you might want to avoid clearly violating the terms of your agreement.

I'm fairly sure that your landlord (unless they are live-in) is required to give you notice before visiting the property. I think they would probably have difficulty proving that you're storing them there if you remove them before any visit.

As a former and occasional landlord, I can see why folks would try to forbid bikes in building. They have a nasty habit of leaving gouges in hallways and doors right about the height at which pedals are when they're carried.

But such things are really best handled under general prohibitions against damaging property and assessing damages against security deposits, etc. etc.

In any case, private landlords have considerable leeway in terms of what we can forbid as long as it doesn't go against anti-discrimination laws. So you may run up against a lathed-plaster wall if you try to go the legal route.

You might be most convincing if you show them your nice little Brompton, all folded up and in a slip cover, and thus not at all likely to bash a huge dent in the owner's 15th century, polished wooden bannisters.