On 2011\01\24 16:27, Jeffrey Smith wrote:

It is, in fact, the Bakerloo Line which runs down Portland Place. The
southbound track runs right under one corner of Broadcasting House.
At Regent's Park Station the line is deep enough to warrant a lift,
but by Oxford Circus it has come close enough to the surface for
escalators to suffice.

I think Oxford Circus was busy enough for the original lifts to be
replaced by escalators, but Regents park wasn't.