In message , Bob Watt
writes

At least two locations on LU have switches which may well be unique to LU,
inasmuch as they can be set with both blades open, when they act as
catchpoints. The locations are a) east end of Earls Court District station,
and b) the turnback siding beyond West Hampstead (Jubilee Line). a
photograph of the latter appears on p.150 of "Principles of London
Underground Operations" by John Glover.

Rayners Lane siding does that too.
--
Steve Fitzgerald has now left the building.
You will find him in London's Docklands, E16, UK
(please use the reply to address for email)