Employer typically will own the bike for the first 12 month lease, but ownership then transfers to the scheme operator if the lease is extended (for peppercorn terms; to maximise tax savings) for the remaining years.
Mention this as, for many, the idea of their employer wanting to take back a 12 month old bike seems quite far fetched. I mean, what are they going to do with them? So the risk of losing out on the value of anything you've paid in cash to an LBS is minimal.
However a nationwide cycle to work scheme operator could feasibly see the value in taking back bikes from the scheme, then flogging en mass.
Cycle to work scheme thread