To use it you have to have a ticket valid on the Underground because you
have to go through an Underground gateline and the route is much slower
and
more convoluted than the above ground way. The weather would have to be
really atrocious for it to be a sensible route when starting at ground
level.

When coming off a ThamesLink train, it was much better and more convenient I
found to transfer to the VictoriaLine.
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