Spanish giant Dragados and a Costain/Vinci joint venture are the last two in the race for the London Underground station improvement project.

The ambitious job to raise capacity at the crowded station has between given a price tag of anywhere between £250m and £500m.

Two strong tunnelling joint ventures of BFK (BAM Nuttall, Ferrovial SA & Kier) and MBA (Morgan Sindall, Balfour Beatty & Alpine Bemo Tunnelling) are now out of the running.

A preferred bidder will now be selected in July with the hope that the final bid price offers big savings on current project estimates.

Under the present timetable site works will start in 2015 for completion at the end of 2021.

London Underground bosses are piloting a new Innovative Contractor Engagement approach to procurement, which will give bidders a share of the saving for innovative designs to save cash on the project.

The process has been designed to encourage innovation, which will be kept commercially confidential so bidders can derive the value and competitive advantage of their designs through the procurement process.

The Bank Station capacity upgrade project will create a new ticket hall at surface level with the successful bidder also carrying out tunnelling work to divert the southbound Northern line running tunnel and build a new southbound platform to the south-west of the existing platforms.

Bank is one of busiest and most complex interchange stations on the network, in the vicinity of busy road junctions and through routes for traffic, next to several Grade 1 listed properties.

The upgrade project will, by 2021, deliver increased capacity at Bank station and a step-free route between the Northern line platforms, DLR and street levels.