However, some cost-saving measures will still be introduced, including staff cuts and the charges to use the research room service in London.

“We have won an important battle. Now we need to win the war for adequate government funding for the Imperial War Museum and indeed all heritage organisations,” said Andy Bye, negotiator at Prospect, which represents the museum’s librarians and specialists.

“Seven days a week for three months, in wind, rain or snow, our members gave up their lunchtimes to leaflet visitors to the museum and collect signatures for the petition.

“Word of the closures was also spread by posters on the London Underground over Christmas and New Year, and the campaign won the hearts and minds of the public, including many high-profile supporters.

“All were shocked at the closure announcement just as the UK was marking the centenary of the outbreak of World War I.

“We thank everyone who signed the petition, the staff who did so much to win these important concessions, those who shared this campaign on Twitter and Facebook and the news outlets who covered this story.”

The museum will also receive £8m across four years to safeguard the immediate future of educational activity. These funds will come from fines levied under LIBOR. However, Prospect remains concerned that the Chancellor has not yet formally confirmed this.

Bye also expressed concern at the research room charges and news that some redundancies will go ahead, though not the 60-80 posts originally envisaged.

“The museum, like others across the UK, has already taken a huge hit from government austerity measures, with funding reduced by 34% in the last five years and more cuts to come,” he said.

“The huge publicity as the election looms has contributed to this climb-down. However, the long-term future of the library’s collections is still not guaranteed – the status of 240,000 library items has been changed so they are no longer part of the core collection.

"The devil may be in the detail and our members will continue to be vigilant about protecting this national resource.”

• Photo by Mark Thomas shows Prospect reps leafleting outside the Imperial War museum as part of their campaign to save the library and education services