On 26 May, 07:18, Paul Terry wrote:
It's not deep enough
Deep enough for what?

the Post Office Railway is on average 21m below
The circle line is only on average around 9m below the surface, so the
PO railway is more than twice as deep.

the stations are virtually at basement level
That's hardly a bad thing. Less distance from the surface is greater
convenience for passengers trying to access it.

the Post Office Railway doesn't have a straight enough alignment - it runs
north of Oxford Street, curving up to Wimpole Street and then coming
back south before the big loop up to Mount Pleasant.

Straight enough for what? The curves are fairly gentle, even though
the tube itself copes with curves like those at Shepherd's Bush, and
the PO railway is close enough to oxford street at all the stations.
It doesn't need to hug oxford street when its not at a station, not
that the current Crossrail's Hanover Square and Dean Street Stations
are on Oxford Street either.

As for the loop at mount pleasant, its a comparatively small thing to
dig a new bypass around the loop than it is to dig an entirely new
route across the whole of london. Besides, mount pleasant /
clerkenwell / essex market could do with a tube station, the met and
thameslink lines run through it but don't stop.