Now, I know a bit about the history of broadgate, and that it used to

be a mainline station called broad street, and assumed that these
might
be the old lift shafts for the broad street entrance to liverpool
street central line tube station, since they seem to be close to
above
where the bridge runs over the west end of the eastbound platform.

I believe they are associated with the Central Line substation, the
cables
to/from which use an old Broad Street escalator shaft. Whether they
correspond to the old lift-shafts I wouldn't like to say.

Ive found this link : http://gallery120232.fotopic.net/p13277473.html
that seems to show an entrance to the tube where the two round things
are.

What confuses me really is the third one out on its own on the corner
by bloomfield street.
It seems a bit too far away from the tube to be a lift or a stair
shaft, and its on the wrong side of the main broad street entrance in
the picture (its about where the chunky sign sticks out) so Im puzzled
what it could possibly be.