Jack Taylor wrote:
For some reason, although it is possible to walk along the
platform from the mainline station to the suburban platform unimpeded, the
LUL gates need to be traversed when accessing the suburban platforms from
the footbridge. Conversely, it is possible to gain access to the LUL
platforms without passing through the barriers by using the mainline access
to the suburban platforms and then crossing via the footbridge!

I've also noticed this - I presume that the gateline had to be
installed further down the footbridge, thus including the suburban
platforms, for reasons of space and safety. But the lack of gates to
get onto the suburban platforms from the mainline concourse (which is
not a secret route - it is a signposted route from the concourse) makes
this a distinctly leaky part of the central London Underground network.

Recently when entering the H&C platforms using this route when I was to
use Oyster Pre-Pay (there are readers on the H&C platforms to touch-in
on), there were revenue protection staff from First Great Western Link
checking tickets on the route from the mainline concourse to the
suburban platforms. As I had no ticket to present to them as such, all
I had to do was say "I'm going on the Underground & I'm using Pre-Pay"
and they let me through, as of course they had to.

I presume that if the tea-cup plan were to be implemented, then
gatelines would be installed on the route from the mainline concourse
to the suburban station, thus eliminating this anomaly.