The £300 million plan to fill the last major gap site in central Edinburgh has taken a step forward with the appointment of world-renowned architects Foster + Partners.

M&G Real Estate announced the appointment for the Haymarket project yesterday. It will be the largest mixed-use development in the west end of the capital.

The four-acre site currently has planning permission for three Grade A office buildings totalling 350,000 sq ft, a 190-room hotel and a 172-room aparthotel. It also has provision for 40,000 sq ft of retail and leisure space.

Fost + Partners has previously worked with M&G Real Estate and Qmile Group, creating and delivering the plan for the landmark £750m Quartermile mixed-use development in Edinburgh.

The Quartermile plan, and its subsequent delivery by Qmile Group, has been recognised with a multitude of awards both nationally and internationally.

Last year, Foster + Partners won the Riba Stirling Prize for architecture for its design of Bloomberg’s European HQ in London, winning best building in the UK – the third time the practice has won the accolade.

Commenting on the appointment, M&G Real Estate’s director of asset management, Aaron Pope, said: “We know from experience that Foster + Partners is a truly world-class organisation. Our success of working with Foster + Partners and Qmile Group on Quartermile, and their continued commitment to providing an innovative, modern and sustainable approach to placemaking, will be key for Haymarket.

“Working with Foster + Partners and Qmile Group we will develop a revised masterplan using the very latest thinking in design, materials and sustainability practices to enhance the impact of the development in this prime location.

“Haymarket will provide Edinburgh with a vibrant place to work, rest and socialise, which we believe will set new standards nationally and internationally. We look forward to revealing our plans for the site in the coming months.”

Located next to Haymarket train station, the development also sits alongside tram and bus services which have links to Edinburgh Airport.

M&G Real Estate acquired the Haymarket site in June last year for £49.1m and appointed Qmile Group to deliver the development.

M&G Real Estate provided £82m to fund the speculative development of the two Grade A office buildings at the site, the six-storey Quartermile 3 and the seven-storey Quartermile 4 in one of Scotland’s largest forward funding deals. The buildings are now home to global financial services business State Street Bank, audio chip designer Cirrus Logic and Canadian fund manager BMO Global Asset Management.

Foster + Partners’ partner Ian Whitby added: “We are very pleased to be continuing our long and successful relationship with M&G Real Estate and Qmile Group with this latest appointment.

“As with Quartermile, Haymarket is a high-profile development and one which will further significantly enhance the fabric of the city, both commercially and socially. Our work on the masterplan is under way.”

Qmile Group chief executive, Paul Curran, commented: “The appointment of Foster + Partners brings together an unrivalled team with the knowledge and expertise to fund, design and deliver what is a key development for the city of Edinburgh.”