A revised scheme for the development, which has been approved by NGS Trustees, has scrapped the extension into East Princes Street Gardens and pushed back the entire project a year for further design work.

Back in March, the project was delayed for “several months” after NGS announced that some aspects of the construction, namely the proposal to build out by an additional five metres into East Princes Street Gardens, were more complex and expensive than originally anticipated.

It has now been decided to remove this aspect of the construction altogether to reduce the cost “significantly” and also lessen the risks involved in what was “an extremely complex engineering problem, extending the building above the main-line railway tunnels”.

While the original extension would have increased further the available display space, NGS assured that the new galleries will still represent a doubling of the existing space to be dedicated to Scottish art in this area of the building.

The Trustees have also decided that there should be a reconsideration of how the collection is displayed within the Scottish National Gallery as a whole, to ensure that Scottish art is presented alongside the international displays. This will mean a completely new presentation of the Scottish National Gallery and an entirely different visitor experience to the site.

All of the other elements of the original project will go ahead as planned including the creation of attractive new Galleries at the Gardens level, new circulation routes within the site and new landscaping within East Princes Street Gardens to facilitate entry into Princes Street Gardens as a whole and the Scottish National Gallery’s Gardens level entrance.

The changes, however, mean that further design work will need to be carried out and new statutory approvals may also be required. Therefore the estimated completion date for the project has shifted from 2019 to 2020.

The exact costs of the longer programme and extra design and project requirements will be determined once the new tender process has been completed, though the aim is to keep as close as possible to the original budget.

Sir John Leighton, director-general, National Galleries of Scotland, said: “NGS looks after an amazing collection of Scottish art and our aim is to provide these works of art with the world-class showcase that they deserve. As with any venture, this project has its fair share of challenges but we are delighted that we can now move forward with plans that maintain our ambition to completely transform the presentation of Scottish art and the experience of visitors to the Scottish National Gallery.”

Cabinet secretary for culture, tourism and external affairs, Fiona Hyslop, added: “I welcome the steps National Galleries Scotland has taken to ensure this ambitious project can be delivered in line with the development’s original aims. Celebrating Scotland’s Art will significantly enhance the visitor experience at this already top-rated attraction, encourage even more people to access and enjoy its iconic collections, and raise the international profile of Scottish Art.”

Hoskins Architects was appointed to the project in 2014.