A key stage of the Farringdon Station project which will lead to an increase in passengers is on track to be completed in December.

Twelve-car Thameslink trains wil run through Farringdon Station from Monday, December 12, once two platforms have been extended. At present Thameslink, which provides services between Bedford and Brighton, operates four and eight-car carriages.

In December, a new large glass-roofed ticket hall for Thameslink and, in the future, CrossRail travellers opens opposite the London Underground entrance.

The technical platform extension work is being carried out underneath Cowcross Street as thousands of comutters pass above everyday.

The construction is complex because it is being undertaken around the 1920s main entrance building which is protected with Grade II-listed status.

Richard Walker, Network Rail project director, said: “This is major level engineering on an old building in a constrained environment next to a very busy live railway and essentially nobody knows what we are doing.

“We have maintained all the Grade II-listed fabric. It will look fantastic.”

Farringdon Station is closed at weekends but remains open during the week.

Since the construction began in 2008 15 Thameslink trains stop every hour up from eight and two new staircases have opened on platform one and two.

Mr Walker said: “We have almost doubled the frequency of passenger services since we started so it has already delivered a great benefit to the area.”