Network Rail has announced the first stage in a project to connect to rail tunnels with the national network.
The scheme will connect canal tunnels in north London, which run between St Pancreas Station and the East Coast Main Line near King's Cross. Network Rail claims this will be the first time local and regional services in various areas have been linked.
It states the connection of these routes will be an important stage in the development of the rail network, forming a crucial part of capacity improvements in London.
Trains using the canal tunnels will be able to provide up to eight of the potential 24 services each hour. These will travel via central London when the £6 billion Thameslink Programme reaches completion in 2018.
Network Rail's route managing director for London and the south east Dave Ward said: "Thameslink will transform the railway across London and the south east, providing passengers with longer trains, more seats and a better level of service to meet the ever increasing demands placed on the rail network."
Part of the project includes longer 12 car trains - which are already used on the line. Stations such as Blackfriars, West Hampsted and Farringdon have also been rebuilt.