is built to impress. The grand staircase is very grand.
A sweeping glory of red carpet, hemmed with banisters and pillars of different coloured marble, all gilded to within an inch of their life.
In the grey of a rainy London morning the chandeliers cast a little light on the scene, designed to awe visitors from around the globe.
also has a red carpet, but the backstairs to the are narrow and are more kitchen unit stone than real marble.
The Lisbon treaty will be signed this week, perhaps even by , and all say that one of its main purposes is to give the European Union a bigger profile on the world stage. But what does that mean for Britain's role?
At the top of the Foreign Office stairs is a series of pictures by .
In them .
In the most imposing, painted after the First World War, America, a tall lass draped in the stars and stripes, head covered with a red revolutionary bonnet, gets a firm handshake.
Martial France, sword in hand and a cock-crowned helmet on his head, waits in line along with Italy clutching the rods and axe that Mussolini had named his party for, and a pretty waif like Japan with flowers in her hair.
Belgium, tattered flag in hand, clings to Britannia's waist, displaying a pert bottom and flowing golden hair.
Serbia, , lies crumpled in a ball.
For those requiring, after all this supplication, refreshment is on hand, in the shape of fruit borne on the head of an African child.
Of course this wasn't a realistic picture, even in 1922 when the painting was hung. America had stepped decisively into European politics, not for the last time.
British rule
There was only a short period when Britain ruled the waves alone. British foreign policy has always been built on a shifting foundation of European alliances.
But does it now need a stronger common European foreign policy? No one I speak to doubts that one of the most important changes in the Lisbon treaty will be to beef up the EU's foreign policy role, by creating a new High Representative: the role that was called Foreign Minister in the defunct constitution.
, Lord Patten, used to be .
It is that job that will be merged with the current role of High Representative to create the new role.
The new High Rep gets commission staff and commission money. He or she will also chair the regular meeting of EU foreign ministers, currently the task of the foreign secretary of whichever country is in the chair for those six months.
Lord Patten says it is right not to call the person the EU's foreign minister. "There isn't going to be a European foreign minister," he says.
"There will be 27 EU foreign ministers and, when they can agree, there will be one person expressing their point of view. The representative will have to represent what the views of the members states actually are, and it is sometimes difficult to squeeze out what those views actually are."
He argues that, whatever the changes on paper, the political reality remains the same.
"The Extremely High Rep, or whatever we are going to call him, has the ability to shape policy if he wants to do it because he chairs the Foreign Affairs Council.
"But while I don't wish to insult 24 nation states, anybody who is trying to represent Europe will have to make damn certain he is representing France and Britain and Germany. If you want to be a High Representative for long, then you'd better be certain you've got those big member states on board."
Reality gap
Lord Patten is scathing about those who he says are worried about "ghosts or noises in the night" and repeatedly refers to the "reality gap", a space in which he believes European dreams and nightmares feed off each other.
Anyone who follows EU affairs knows exactly what he means. European enthusiasts paint a vision of a future and eurosceptics react as though it has come to pass.
But when it comes to the High Rep, it's understandable that those suspicious of further integration worry about "mission creep".
There are still very big questions about the role, which will only be settled next year. Slovenia's ambassador has already said that .
Many of the details are, well, details. Complex and abstruse. But there is at least one bit that sounds wonkish but really matters. Will the High Representative, who after all will be a vice president of the commission, have the "right of initiative" that other commissioners have?
In plain English, will he or she be the servant of the nation states, or to a certain extent give them the lead?
British sources say the HR won't have the right to make or propose policy. Others disagree. Lord Patten says: "There is some lack of clarity.
"It's surprising that, while the Foreign Office have been nervously looking over their shoulder at what critics in the Telegraph or Times or Daily Mail are saying, they haven't sorted out those issues rather more clearly.
"At the moment, it seems to me one of the two or three questionmarks over the role of High Representative. He's not only chairman of the foreign ministers' Council but is also able to initiate policy and deliver papers to it.
"When I was a commissioner I initiated policies in some sectors but I didn't chair the council and I think there is at least a question over that."
Real world
Javier Solana, the man who is currently doing the job, has no doubt whatsoever when I ask him about this. He says: "He will be a member of the commission. Not only that, he will be part of the Council. As a member of the commission he will have all the rights attached to that position. The policy has to be adopted by the Council but he will have the right of initiative."
This is important but is perhaps pretty abstruse. What about the real world?
It has been notoriously difficult to find agreement on Kosovo, where some countries, like Spain and Greece, are worried about the knock-on effect of recognising a break-away province as a nation state.
Mr Solana's answer shows he thinks the difference will be in efficiency on the ground, rather than the making of policy.
"It will be very different. There will be a channel that can mobilise all the resources of the European Union. In Kosovo there are many problems that doesn't stop with its final status. We have to get an employment law, more energy, a more dynamic economy. People there need a lot of help. And the manner in which that help is given will be handled in a more coherent manner."
Lord Patten seems to agree: "Is the appointment of a Very High Representative going to make any difference in Afghanistan? Is it going to make any difference to whether we've got any policy in the Middle East?
Political will
"Unfortunately, I rather doubt it because you are talking about political will. I think the main plus to come out of this will be to pull the back office and the front office more closely together.
"It's become more and more apparent to me, when I was working in Brussels, that much of the real agenda of foreign policy these days isn't those age old questions of "The Eastern Question".
But the real issues are the impact of the environment on foreign policy, water management on foreign policy, epidemic disease on foreign policy, organised crime and the drugs trade on foreign policy.
"Those are areas where the commission has some responsibility. If you related that to the traditional discussion of foreign policy you might get rather further than we get at the moment."
He's dismissive of those who worry about a loss of British sovereignty: "The biggest issue to effect our sovereignty in the last few years has been our commitment in Iraq; without having any real say over what was happening there; which British servicemen and women were being shot at and being killed there.
"That is a huge sovereignty issue. Nothing, nothing, that happens in the European Union is going to be anything like that in its dimensions."
Is he right? Do we fuss about giving up sovereignty to the EU within a formal structure and not bother if it is handed to America? What about the other issues? Please do comment (and sorry if once again the technology has been creaking a bit).
Tomorrow William Hague's view of foreign affairs and the Treaty.