The chief executive of Network Rail has told ITV News that lessons have been learnt after last year's disruption.
He says he's confident that the Christmas engineering work in and around London will be completed on time.
Disruption could continue for up to a week as 20,000 engineers work to upgrade the lines.
Currently, services from Brighton and Gatwick to London are affected.
There are no Southeastern services to London Bridge, Cannon Street and Charing Cross.
Paddington is now open, but half of the tracks are closed for work on Crossrail causing disruption.