I believe RW23 is currently not an operational runway - it has one of BA's Concordes sat just beside it, and is used as a taxiway at the moment.
Notams for EGLL show the following:
RWY 23 CLOSED DUE WIP 25 APR 15:40 UNTIL 30 NOV 23:59
DME HTT ASSOCIATED WITH RWY 23 UNSERVICEABLE 31 DEC 19:47 UNTIL 31 DEC 23:59 2004
Hope this helps!
Leon