I've got some chrome forks, and there's a few small patches of rust, but one patch, maybe the size of a thumbnail, that is flaking. I can take the rust off and, I'm pretty sure it won;t show, but how do I stop it coming back. Is carefully applied varnish the only way to go, or is there something else that can seal the metal from the elements?

Not much you can do about flaking chrome.
Keep the bare metal clean and either put some clear fingernail polish on it or keep a thin coat of oil on it.
If you keep it clean and dry after each ride, it won't get any worse.

Clear fingernail polish or, a coat of car wax or, Blue Magic metal polish.

Thanks for that, chaps. I never thought of car wax.