So it has finally come to light why the Waterloo & City line has been repeatedly breaking down since it reopened. Metronet didn't replace the signalling system during the five-month-long upgrade because its contract with LUL didn't require it to.
The Evening Standard is scandalised by this, and points out that it is all the fault of the Public-Private Partnership (PPP). Quite right, but really quite hypocritical. We seem to remember that every time we went on strike to try to stop PPP, the Evening Standard described us as something worse than vermin.