The UK’s Transport for London has estimated that the underground rail upgrade will cost £721m, which is more than 2.5 times the original estimate of £285.3m proposed in 2002.

In 2002 private firm Tube Lines claimed the upgrade would cost £285.3m, but Transport for London, which took over the work, has now revealed that the final project cost was £721m.

Work on the Jubilee line was expected to be completed by the end of 2009, but in reality only finished this July.

The bulk of the £614m investment was spent, under the PPP arrangements, by Canary Wharf-based Tube Lines consortium, which was responsible for carrying out the upgrade.