A final victory: Winston Churchill is given a dedicated museum 40 years after his death

He steered the nation through its darkest hours in the Second World War and was named the greatest Briton of all in a BBC poll. And now, 40 years after his death, Sir Winston Churchill is to be honoured with a museum in his name.

Next month, the Queen will officially reopen the underground offices from which Churchill directed wartime operations in London as the Churchill Museum and Cabinet War Rooms after a £6m expansion to create Britain's first museum dedicated to the statesman and writer.

The existing Cabinet War Rooms opened in 1984 and were expanded two years ago to offer visitors a view of the suite of rooms Churchill used with his wife and staff. But there has never been a proper display of his life story, and even at the family home at Chartwell, Kent, there were only a couple of rooms dedicated to him. The new museum is housed in 850 square metres of new galleries next to the War Rooms.

Phil Reed, the centre's director, who had the idea for a dedicated museum a decade ago, said now was a good time to reflect on the former prime minister's life. "Forty years on is a good point to put a museum together," he said. "It is a good interval to be able to judge someone's place in history; deciding whether someone is great or not is better understood when you're decades away from their life and death.

"I think there's no question he was great, but the thing about greatness is nobody is great their whole life. This exhibit will help people understand Churchill the man, his humanity, the feet of clay. What we are trying to do is to prompt people to think more about him, to learn more and formulate their own opinions. The 2002 Greatest Briton poll showed Churchill is immensely popular in this country."

Lady Soames, Churchill's daughter and among the members of the family who have raised funds for the new museum, said she was thrilled. "As time goes on, it is tremendously important to put not only him but the times he lived through in perspective in a way that will grip people," she said. "It's history and rapidly becoming old history. We've been hunting out all sorts of things the family are going to lend. There will be things that are intimate and personal to him, but it will also be much wider. We want to put these wonderful walls [of the Cabinet War Rooms] in their context."

The family is lending items, never seen before in public, including the baby Churchill's ivory rattle and christening gown, the engraved silver-covered volume he was given when he won the Nobel Prize for Literature and several of his paintings.

Others revealing more of Churchill than the defiant orator with the trademark cigar and V-sign will include the school records showing punishments he suffered at Harrow, his copy of the 1883 Boys Own Manual and a gun he had during the Boer War when he escaped from a prisoner-of-war camp.

Visitors will be also able to stand next to the wartime door of No 10 Downing Street through which he used to pass. This item was among many scavenged, with government support, by Mr Reed and his staff from the Treasury buildings that lie above the museum.

Gordon Brown, the Chancellor, last year formally handed over the red budget box which Churchill used when he held the post in the 1920s. Entrance will cost £10, an increase of £2.50 on present charges, because it provides access to the War Rooms and the Churchill Museum. The new attraction, which opens on 11 February, is expected to add at least 50,000 visitors a year to the present attendance of 300,000.

Backers need to raise £6m more for an endowment fund to secure the museum's future. Americans have given $1.5m (£80m) towards capital costs and the same for the fund.