Interserve and Tiger Developments entered into a joint venture agreement in last April to develop the four-acre site next to Edinburgh’s Haymarket station.

Agreement has now been reached with Network Rail to start preparatory works as early as December on the railway tunnels beneath the site.

The tunnelling work signals the start of one of the city’s most important development projects of recent times, resulting in a £200m mixed-use development delivering a mix of high quality office, hotel and retail space with the potential to create 3,500 jobs.

The Haymarket has full planning consent for 404,000 sq ft of office accommodation and 60,000 sq ft of commercial and leisure space, together with a 165-bedroom hotel and a 320-space underground car park.

Interserve’s Development Director David Westwater said: “This agreement with Network Rail to start work on the site represents a significant milestone for one of Edinburgh’s last remaining gap sites.

“We are looking forward to completing the underground works during 2014, allowing for above-ground construction to start in early 2015.

“We are looking forward to starting what we believe to be one of the best city centre development schemes to be found anywhere in the UK right now.”

On-site construction is set to start in spring next year, with the first buildings’ phase earmarked for completion in 2016.

The construction project alone will be worth £150m and will be delivered by Interserve’s local construction team, based in Livingston.

Tenants already signed up for the initial development phase include Q Park, Tesco and serviced apartments provider Staycity. Food chains Prezzo and Pret A Manger are already committed to the second phase, together with advanced discussions with other occupiers for a further 70,000 sq. ft. of retail and office space.