This week, in a West London swimming pool, I watched as two large West African women plunged into the water topless in their knickers. No one commented until one woman said: "They look like they're having fun." It was only when they went into the cafe afterwards and one lit a cigarette in a no-smoking zone that someone complained.

This sums up the British. They are a tolerant nation who enjoy their diversity but like to stick to the rules. In the last few weeks, as the threat of bombs has escalated, this has become more apparent.

They have made it clear that they appreciate their multi-layered culture but are horrified that children born in Britain could violate their own country.

There is a rising sense that if you live in Britain, there are certain values by which you should abide. Where once patriotism was seen as more embarrassing than pornography, the British are now beginning to feel that the only way to hold this country together is to give everyone a motive to want to belong, and a reason to be proud of owning a British passport.

The Union Jack is no longer seen as a symbol of the far Right, Our Island Story is now making a comeback, people want to sing Land of Hope and Glory. This is not about jingoism. It is to do with being confident about who you are.

After years of being embarrassed about having a past and an empire, the British are beginning to realise that it is vital to be proud of their heritage and to be enthusiastic about what their country can achieve in the future. Self-hatred only breeds more self-hatred.

The suicide bombers seem to have adopted the worst aspects of Britishness - the self-loathing yob and the dependency culture - rather than embracing Britain's real benefits.

So what does it mean to be British? Jacques Chirac thinks it's about bad food. Tourists cite Buckingham Palace and the double-deck bus - which has become even more iconic since the bombings. The series Little Britain shows a nation of eccentrics with a sense of humour. According to the Australians, the British always lose at cricket. Others told me that, for them, Britain was all about curries, roasts, toast, kettles, gardens, gnomes, tea cosies, rain, the Queen and her corgies.

Statistically, the country is divided in each census into the English, Welsh and Scottish, into ethnic minorities, and into religions. But Britishness is about more than this. It is what unites, rather than what differentiates us, that is particularly interesting.

Until recently, the Government was keen to play down Britishness, with Labour's Lord Parekh insisting that the country is now "a community of communities". Now, multi-culturalism is no longer seen as the answer. Nor is Cool Britannia, which promoted the new but sneered at the old.

At the end of the last century, the emphasis was on devolution and the rise of single faith schools - but it is now clear that nationalities and religions need to be bound together if Great Britain is to survive.

Jeremy Paxman, author of The English: A Portrait of a People, says: "Britishness was an imperial identity to bring the Empire together. Our biggest problem has been redefining it for the post-imperial period. But it is an incredibly useful concept because it is so encompassing - you can be Scottish-British, Muslim-British or Pakistani-British."

The Government, which has been criticised for attacking British institutions, is now keen to promote a deeper concept of Britishness. Gordon Brown wants "a patriotic vision of Britain's future as a country of ambition and aspiration". David Blunkett, who as Home Secretary introduced citizenship ceremonies, says: "We needed to reinvent Britishness as a reaction to devolution and multiculturalism. If we lose our sense of belonging and become fearful of other cultures and religions, that's when we become racist."

The Tories are also returning to a favourite theme. Michael Howard, the Conservative leader, says we must promote the "British dream". David Davis immediately knows what being British means to him. "I'm a big believer in the power of the Anglo-Saxon set of institutions that we have exported around the world and in our sense of freedom." David Cameron, another probable Tory leadership contender, says: "We need a common past, present and future."

Religious leaders are also preaching Britishness. The Chief Rabbi says that Britishness is incredibly important for Jews. "We recognise in Britain one of the most tolerant countries in the world. We sing the national anthem at all our gatherings. We say a prayer for the Queen and the Royal Family every Saturday in the synagogue."

Muslim leaders want guidelines. Inayat Bunglawala, of the Muslim Council of Great Britain, says: "I wish there were such a thing as Britishness to bind our segregated society together. It should be about having the right to practise our faith and move freely, but also a responsibility to care about this country."

The boxing champion Amir Khan says: "I'm Asian but I'm British. I was born here, I went to school here, all my mates are British and I am proud to represent my country."

Sir Trevor McDonald, who is seen as quintessentially British, says: "If you are born in a former colony and educated in a way which was equivalent to a minor public school, there is a sense of Britishness in your DNA. It's a sense of fair play, social and legal justice; it's also a sense of magnanimity. You don't gloat about your moment of victory."

Immigrants are seen as a vital way of reinvigorating Britishness.

Susie Symes, who runs the Museum of Immigration, says: "The push factors are obvious - immigrants have had enough of their own countries. But we rarely talk about the pull factors that bring people here: immigrants are drawn by the freedom and tolerance."

John Koh, a Singaporean who co-owns two British companies - the antiquarian booksellers Bernard Quaritch and Spink, says: "The British are very good at finding contentment with their hobbies and their DIY. They like to get a balance in life: they never work too hard or play too hard. They don't like extremes of behaviour. The only problem is that whenever you sit down to watch your teams play sport, you always have that constant dread that you are going to lose."

Emma Soames, the editor of Saga magazine, says that the older generation has a very strong view of Britishness. "Ginger beer, James Bond, pony club camp, a deep love of animals and an ambivalence towards children. We also have a great sense of pageantry and dressing up which we mustn't lose."

British historians are aware of the rekindled interest in Britishness.

Anthony Beevor, author of Stalingrad, says: "Britishness is a fairly recent phenomenon but, if it stands for anything, it's a sense of fair play that goes back to the Napoleonic War. There has never been a doctrine of Britishness. Unlike the French, we are too embarrassed to talk about ourselves seriously. If we do, it is as a parody - dinner jackets and Oxford marmalade."

Andrew Roberts, author of a biography of Lord Salisbury, says that Britishness is easy to define. "We have a profoundly different history to the rest of the world - partly because of our geographical insularity, partly because we are the most constitutionally mature. We were the first to have an industrial revolution and we don't lose wars. We once covered one quarter of the world. Of course, we are unique - we shouldn't be ashamed about our past."

Tristram Hunt disagrees. "The Conservatives have been allowed to define Britishness because the Left got too sucked up in multi-culturalism. But Britishness shouldn't be about the Empire - it's about freedom of speech, public dissent, and institutions like the Open University."

So what do foreign correspondents think of the British?

Sarah Lyall, of The New York Times, says: "It used to be about the stiff upper lip, cream teas and cricket, but all that changed after Princess Diana died. The British don't have an obvious set of values now other than their knack for self-depreciation."

Brooke Shields, the American actress now appearing in London, thinks its easy to define. "Fudge and pubs." But Britishness is not about just a set of values or sweets - it is also about the people who have made Britain.

Baroness Susan Greenfield, the director of the Royal Institution, points to the fact that Britain produced Newton, Darwin, Watson and Crick, and has won more Nobel prizes than any country except America.

The British are also great innovators, explorers, story-tellers, soldiers and sailors - a tradition carried on by Ellen MacArthur sailing round the world, Tim Berners-Lee inventing the internet and J K Rowling writing about Harry Potter.

Charles Saumarez Smith, the director of the National Gallery, admits that the British do not admire intellectuals in the same way as the French - they are wary of sounding pretentious. "But we can still inspire world movements like BritArt."

And the British hope, now that they are holding the Olympics in 2012, that they can become a great nation of sporting heroes again.

The British love of the countryside, the seaside, wet picnics, fishing, rambling and bird-watching is one area that the Government has so far refused to celebrate.

Clive Aslet, the editor of Country Life, says: "Britain has always had a pastoral theme - in music and art - and there was always a yearning for the countryside. Now, it's more like war between town and country."

Rory Knight Bruce, who has been master of foxhounds three times and is the author of Timothy the Tortoise, the Remarkable Story of the Nation's Oldest Pet, (a very British book), says: "We've become more supine and we won't stick up for ourselves. Kindness and duty are trampled over, and the countryside is dismissed as irrelevant."

Another British way of life that is disappearing is the House of Lords. Lord Strathclyde, the Tory leader in the Upper House, says: "Many of our greatest institutions are being battered by this Government but we are a resilient nation: as long as we keep celebrating Shakespeare, Wordsworth, Coleridge, Milton and the King James Bible, we'll survive."

And people are beginning to embrace again what makes them feel good about being British.

"It's about being classic with a twist," says Geordie Greig, the editor of Tatler magazine. "About combining the best of British with abroad, having Zadie Smith and Shakespeare, Kelly Holmes and Paula Radcliffe, Ikea furniture and castles."

Mriganka Chatterjee, one of the first to take the new citizenship test, says: "I could have chosen worse," showing another British trait - understatement. Even if you are proud to be British, you should never brag about it.