A TWITTER hashtag has been used to mark the final stages of redeveloping the front of King's Cross station in London.

The square which will replace the old 1970s concourse will open to the public next week, completing the £400 million upgrade of the station.

Opened in 1854, King's Cross was given a sprawling 'temporary' concourse in the 1970s, which has only recently been demolished and replaced by a much larger structure on the western, or St Pancras side, of the main trainshed.

As the countdown to the opening of London’s newest public space continued, the people who designed and built King’s Cross Square gathered at the site this weekend to create a giant visual memento visible from the air.

A helicopter came down to 150 metres to allow photographs to be taken. Project managers and architects stood shoulder to shoulder with pavers and demolition staff, with other props and materials including pieces of high visibility clothing laid out to spell out '#KXSQ’ -- the Twitter hashtag Network Rail is using to circulate updates and information about the project.

Tom Fernley, a project assistant at Network Rail, started his career on the project and is now celebrating his seventh year.

He said: “The redevelopment of Kings Cross has been a landmark project not only for London but for Network Rail, and these celebrations have been a great way to extend thanks to the people that have made it all possible. We have managed to mark this moment in history by creating an impressive memento to savour for years to come.”

The new 20,000 sq metre Kings Cross Square will open on 26 September when, among other benefits, the full 1854 facade will be revealed again. The station is used by 28 million people annually.