Offramp wrote:

My memory is that the first deadline was 2001 or 2002, but that a
general media surge suggested to punters that New Years Eve 1999/2000
was the deadline.

It was certainly late - I remember the 1994 tube maps predicting a 1997
completion date and throughout 1998 & 1999 there were reports of further
delays - Westminster station was especially problematic and initially the
extension opened as just a separate shuttle service from Stratford to North
Greenwich, later Bermondsey then Waterloo.