Foulds attributed this to the rush to complete the extension by 2000, which led to the use of temporary remedies.
He said: "A lot of the original design work was never completed. There was a patch-and-mend interface put there instead."
Foulds said the consortium has had to install added insulation on tracks to improve the connection between the two signalling systems.
Problems on the Jubilee Line contributed to the failure of Tube Lines to meet one of its three performance measures for the first year of its PPP contract: customer delays caused by infrastructure failures.
The other two, which the consortium did meet, were station maintenance and cleanliness.
Foulds said that the consortium would be changing the procurement of its station upgrade work. It had inherited a framework involving suppliers Gleeson, Gee and YJL. It will change this to a series of discrete packages.
Foulds said: "We want to get a production line mentality for stations work. We also want to bring more design in-house."