The threat to the museum is outlined in Prospect’s formal response to IWM management’s proposals to plug a projected £4m annual deficit, which resulted in large part from government cuts to grant-in-aid.

The submission highlights the proposed closure of museum’s world-renowned library and hugely-popular Explore History facility as being particularly damaging. The submission coincides with a new year advertising campaign on the London Underground to highlight the museum’s plight.

Andy Bye, Prospect negotiator, said: “The museum’s vision to promote the understanding of both the causes and consequences of conflict cannot be fulfilled if the library is closed. It’s a simple as that. More than 18,000 petition signatures collected in just a few months show the public agree.”

The unique library collection is the most used resource by visitors to IWM’s Research Room and a vital source of information for the museum’s historians, conservators and curators.

Opened in 2010, Explore History is a specially-designed public space giving anyone free and convenient access to photos, film and sound recordings as well as documents, art and books. IWM's London site attracted 55,000 walk-in inquiries from visitors in 2013-14, even though the museum was closed for a significant length of time.

Prospect’s submission also warns that if the closures go ahead, IWM will no longer be able to meet the requirements of the Arts Council accreditation scheme for UK national museums. These stipulate the provision of study and research facilities for academic and public use.

The union suggests that instead of proposing closure, IWM management should have taken steps to raise income through the greater use of donation boxes, selling photograph permits as well as museum tours, workshops and courses. The submission points out that many other museums, such as the Science Museum, have made great strides in encouraging visitor giving.

Prospect says that projected savings of £300,000 a year do not justify the closures and that the costs of implementation have not been accounted for.

Part of the recently announced government funding of £2m a year for the next four years – earmarked to safeguard education services at IWM’s Duxford, HMS Belfast and Churchill War Rooms sites – should also be used to keep the library and Explore History open, it suggests.

“It is vital that visitors are encouraged to donate as much as possible in the current financial climate and other museums and galleries have made much greater effort in this regard. These efforts have yielded positive results and show that cost saving plans put forward by IWM’s management are ill thought out and short-sighted,” he added.