By Martha Kearney Political Editor, Newsnight

Mr Brown is calling for a debate on 'British values'

Gordon Brown lays great stress on the importance of looking to the long term. That's certainly been the case with this film. It took around six months to get the green light and we have been filming since January.

Now, in the week of the budget, we are broadcasting a long film which explores Gordon Brown's ideas about Britishness.

This isn't simply a question of national identity. It becomes increasingly apparent that these ideas are underpinning an entire political philosophy . He talks to us about the constitution, education policy, the UK's relationship with Europe and the United States and multi-culturalism.

He also says that this will be the theme of his Budget: "We need to have this debate because - and this is the theme of my budget in the next few days - you cannot, as a country face up to the huge decisions that you've got to make in the modern world - unless you do have a sense of shared purpose, an idea of what your destiny as a nation is."

'Values, not institutions'

The starting point, according to the Chancellor, is values rather than institutions.

At the Great Britons Awards early this year he said: "We can find common qualities and common values that have made Britain the country it is. Our belief in tolerance and liberty which shines through British history. Our commitment to fairness, fair play and civic duty."

I think the days of Britain having to apologise for our history are over; I think we should move forward Gordon Brown

At this rather glittering occasion we asked various celebrities for their thoughts on Britishness. Look out for Lawrence Llewellyn Bowen. And David Starkey was rather amused: "Fair play is important but we also have a sense of oddity and intense competition.

"I mean, dear me, look at Gordon Brown. Tough, brutal and ruthless as old boots. Does he believe in fair play with a political opponent? I say, doctor heal thyself."

That does rather raise the question of why Gordon Brown is talking about national identity - more the role of a Prime Minister than a Chancellor.

Mr Brown says we shouldn't interpret his views on Britishness as setting out a prime ministerial platform

I put to him that this was an attempt to show that a Scot could become a Prime Minister: "Does this relate to your own personal ambition, people have said that the reason that you're looking to the British question is that post devolution it would be very difficult for a Scot to become Prime Minister?"

He replied: "I actually fought the Nationalists in Scotland very hard and I put the case, like others, for there being a United Kingdom. It's right for me to say at the audiences that I talk to: 'Let's have a stronger sense of who we are as Britons and let's see whether we can build a common ground'."

I then asked if he could understand why people might think that this is setting out a Prime Ministerial platform.

Mr Brown said: "I don't think people should see it that way at all, I mean I've always said that what you do in the job you're in is more important than the job you hold."

Britishness is certainly a subject which has interested Gordon Brown - who has a PhD in history - for some time. We visited his birthplace of Kirkcaldy in Fife where he was attending the annual Adam Smith lecture. There he told me that growing up by the sea had shaped Adam Smith's views on free trade and his own conviction that Britain as an island has an internationalist outlook.

Empire hangover?

More controversially he told our crew in Tanzania that it was time to take a new view of Empire.

"I think the days of Britain having to apologise for our history are over. I think we should move forward. I think we should celebrate much of our past rather than apologise for it and we should talk, rightly so, about British values.

Gordon Brown has stressed the need for more history teaching

"If you look at whole span of British history it's time to emphasise that that is at the core of our history, that's at the core of our Britishness and it's such a potential influence on our future that I believe we should be talking about it more not less."

The Labour peer Bhiku Parekh took exception to that.

"For Gordon Brown to say we have nothing to apologise for, that's too rosy, one-sided a view of empire which is false and rather insulting to people who are its victims because these people who felt pain and tragedy are brushed aside. In the case of Mau Mau, for example, we set up concentration camps, people were tortured."

Others have been critical from the right by the likes of Roger Scruton, author of England: An Elegy, who argues that the impact of Labour party policy on Britishness has been largely negative. In particular, he believes that devolution has fragmented our loyalties.

Gordon Brown himself hints at the need for further constitutional change including reform of the House of Lords. He stresses the need for more history teaching and calls for it to be compulsory till the age of 16. He also wants learning English to be compulsory for those on job seekers' allowance.

For Kremlinologists of the Brown-Blair relationship, there are certainly some interesting coded messages beyond the intriguing fact of a Chancellor ranging quite so widely in the first place - he laughs when I suggest this is "Brownism".

He rejects the idea of the Cool Britannia of Tony Blair's early years. More seriously he is critical of the idea that Britain can be a bridge between Europe and the United States - an idea which Tony Blair has made his own.