A fundraising campaign for £370,000 was launched last night to help bring what is widely believed to be the oldest complete civic building in England back into use.

The Guildhall Project aims to turn the Grade I-Listed Guildhall in Bury St Edmunds, which has not been open to the public for 40 or 50 years, into a heritage centre, but, far from being a museum, it hopes to be a “varied and interesting” experience for people, with virtual reality and re-enactors in places.

The building had served the community continuously for more than eight centuries, with its uses including a meeting house, a court of law, an infirmary, and during the Second World War it became a regional headquarters for the Royal Observer Corps, a vital operations room supporting the RAF during the Battle of Britain and beyond.

Lat night, there was a showcase event at the building, in Guildhall Street, to launch an appeal to raise £370,000, which is needed as match funding towards a Heritage Lottery Fund (HLF) bid that will be submitted in September.

The project, which will cost almost £1,600,000 in total, has already raised funds or has cash pledged to the tune of £468,000.

Air Vice Marshall Mike Jackson, project director, said everyone was “absolutely committed” to getting the project done.

He said: “We are unique in three ways: we are the oldest civic building, the timbers in the roof are from the middle ages and, if not unique, are extremely rare, and the Royal Observer Corps operations room is the only one left out of 40 that were built.”

He added the project was notionally linked with the British Museum and the Battle of Britain museum, Bentley Priory, and was looking to join other heritage trails to bring money into the town.

The 8th Marquess of Bristol, Frederick Hervey, who spearheaded a £1.2million restoration project at Ickworth Church at his family’s ancestral home, the Ickworth estate, was guest of honour at the event.

He said: “I think it’s important buildings get used. I think it’s a great project, and I will do anything I can to support it.”

The project aims to return the building to widespread public use after a programme of conservation and renovation works.

The plan for the Guildhall includes presenting the World War II operations room as it was at the height at the war and a ‘time gallery’ in the entrance hall, giving people the chance to view clocks from the Gershom-Parkington collection.

Sarah Grieveson, fundraiser for the project, said there would be temporary exhibitions in the building, and emphasised the idea was very much to get the local community inside once again.

The Guildhall Project is led by the Bury St Edmunds Heritage Trust, supported by the Guildhall Feoffment (freehold trustees of the Guildhall) and St Edmundsbury Borough Council (administrators and managers for the building).

The initiative was awarded £73,600 of initial support from the HLF in 2013.

To support the fundraising appeal contact Ms Grieveson at sarah.grieveson@btinternet.com