In message , DW
downunder writes

So I take it these extra 2 tunnels, total 5 tracks, connect to nowhere
but could be useful storage, or wartime propaganda command HQ ...

They were leased from Network Rail by a property company some years ago,
and the latest I heard is that the MCC (who lease the ground above)
intend to enter into partnership with the new owners to redevelop the
site for flats, which they hope will pay for the redevelopment of Lords.

--
Paul Terry