On 14 Jan, 04:35, wrote:
There was an exit at the extreme rear end of the EB Central Line
plaform. You went up stairs then turned right into a corridor which
lead due north to reach the lifts lower landing. At top level these
lifts allowed access directly onto the concourse of Broad Street BR
station. All this was still there disused until the Broadgate Centre
was built in the mid-1980s.

That makes sense. It would have to be at that (ie south) end of the
Central Line platforms. Presumably the passage leading to it was
tucked behind where the main escalators still are.

Do you know when it was last in use?