"Tony Polson" wrote

When Network SouthEast was formed, there was a budget for paint to
relivery the trains and stations, and not much else. Against that
background, the re-opening of the Snow Hill line, the construction of
City Thameslink station and the tunnel up to Blackfriars, and the
building of the Class 319s, represented another fine achievement.

IIRC part of the original business case for Thameslink was saving in stock
by not having trains hanging around at Central London termini. Part of the
business case for City Thameslink, and going under rather than over Ludgate
Hill was the value paid to BR for unlocking land for development.

Peter