The much-anticipated reopening of Norwich Castle's historic keep has been delayed until after the summer.

Museum bosses confirmed they had been forced to rethink the multi-million-pound work to transform the Norman-built landmark due to "unexpected discoveries".

It is a blow for museum chiefs, who had hoped, after four years of work, that the revamped keep would be open in time to attract tourists over the summer season.

Eastern Daily Press: Work on Norwich Castle's keep started in summer 2020Work on Norwich Castle's keep started in summer 2020 (Image: Denise Bradley)

A Norfolk County Council spokeswoman said: "The redevelopment of Norwich Castle is a challenging and complex project, taking place within a very sensitive Grade I listed building and Scheduled Ancient Monument that has been in constant occupancy for over 900 years.

"As a result, unexpected discoveries relating to the historic fabric are still being made as the final areas are opened up.

"This means that the project’s architects and structural engineers have had to adjust some of their proposals to ensure that the right choices are being made to minimise any impact on the historic fabric of this medieval structure, as we transform the castle into a dynamic but sensitively restored heritage landmark for all to admire."

Because the building is protected, any change to the original plans needs to be approved and signed off by watchdogs Historic England and Norwich City Council.

The work, which started in August 2020, will see the keep transformed, with a new medieval gallery featuring objects on long-term loan from the British Museum.

The ambitious project, which museum bosses hope will attract 100,000 more visitors to the castle each year, is recreating the keep's original 12th-century layout.

Eastern Daily Press: How the revamped Great Hall in Norwich's Castle Keep could lookHow the revamped Great Hall in Norwich's Castle Keep could look (Image: Haley Sharpe Design)

READ MORE: See inside the £15m revamp breathing new life into Norwich Castle

The original floor levels, from 1121, when King Henry visited the castle, are being recreated - a task which has required the knitting together of hundreds of tonnes of steel frame to bear the load of the new floors.

Other changes include a new glass bridge and lift, which will mean everybody can get access to all floors of the castle, including the battlements.

Eastern Daily Press: A visualisation of the new look battlements at Norwich CastleA visualisation of the new look battlements at Norwich Castle (Image: © COPYRIGHT FEILDEN+MAWSON LLP)

New toilets have already been installed and the project, known as Royal Palace Reborn, will also see a new cafe and shop created.

When revamp work on the castle started, the ambition was for the new-look museum to open in 2023.

Eastern Daily Press: A visualisation of a new bridge that will provide direct level access to the principal floor of Norwich Castle keep, revealing currently hidden views of the Bigod Tower and east façade of the keepA visualisation of a new bridge that will provide direct level access to the principal floor of Norwich Castle keep, revealing currently hidden views of the Bigod Tower and east façade of the keep (Image: Feilden + Mawson)

But Covid and delays in getting the materials needed have, on a number of occasions, pushed back the keep's opening date.

However, the Castle Museum and Art Gallery have remained open throughout the work and another section - albeit not the keep itself - will be opened this summer.

Eastern Daily Press: A visualisation of the ground floor of Norwich Castle's keepA visualisation of the ground floor of Norwich Castle's keep (Image: Haley Sharpe Design)

A spokeswoman said: "We currently hope to open the Percival Wing of the building to visitors in early summer.

"This will include the striking new entrance doors leading to our new entrance atrium that gives visitors spectacular views of the east face of the Norman keep which have been hidden for many decades.

"Also opening to visitors will be our new shop and our new café restaurant. We will also be opening a new learning space for use by schools and other groups."

But in the meantime, an opening date for the keep has yet to be announced. And it is not clear what the impact on the cost of the project, which has received almost £15m of National Lottery funding, will be.

The spokeswoman said: "We are working with our project partners on finalising an opening schedule for the keep itself, with the aim of welcoming visitors as soon as possible.

"This will include the recreated Great Hall and royal apartments of the Norman kings, our exciting new British Museum Partnership gallery and the new rooftop terraces that will give panoramic views across the city centre."