The green light has been given for ambitious £13m plans to transform Norwich Castle's historic keep.

The National Lottery Fund announced last month it would contribute a further £9.2m towards the Gateway to Medieval England project.

The project will see the 900-year-old castle's keep re-imagined as it was in its heyday as a palace for Norman kings, ensuring the castle is seen as a world class attraction.

There will also be a medieval gallery, in association with the British Museum, along with changes to access and new lifts.

But, despite the funding boost, a hurdle which still needed to be cleared was to obtain planning permission from Norwich City Council.

That permission was unanimously granted at a planning committee today.

The building is Grade I listed and of 'international significance' and The Victorian Society had 'strongly' objected to the proposal.

They were concerned about the removal of the keep's 19th century balcony, which is the work of Victorian architect Edward Boardman.

But Dr Tim Pestell, curator of archaeology at the castle, told members of the planning committee that Boardman himself had aspired to restore the level of the original keep, but had been thwarted in doing so.

He said: 'Most people who visit the keep find it incredibly hard to understand the castle, which was what they came to see.

'This is a unique opportunity to breathe new life into the castle and make it fit for purpose for the 21st century, rather than fossilised in the 19th century.'

Officers had said there would undoubtedly be harm caused to the building by the revamp, but that the public benefit of the work outweighed that harm.

In granting permission, city councillors welcomed the revamp.

Liberal Democrat leader James Wright said: 'I think this is a very exciting proposal. Not withstanding the real concerns about Boardman's work being undone, the overall benefit is the long term use of the castle is secured by this proposal.'

Labour's Mike Sands said: 'Buildings are dynamic. They do change and we need to keep that in mind.

'We have a responsibility to preserve, yes, but also to keep it a dynamic building that moves into the future.'

Now that permission has been secured, work could start as soon as next summer.

Museum bosses have pledged the castle will remain open during the work, with the revamp being done in stages.