YES. His presence would improve the global credibility of the EU

On current trends, the 21st century looks like being dominated by a "G2" of the US and China. That is not good news for Europe. The US and China (like most other powers) are sometimes unilateralist and lack Europe's enthusiasm for strong international rules and institutions. If the EU wants to send a signal that it intends to play a role in shaping the new world order, it should appoint Tony Blair as its first president.

The likely ratification of the Lisbon treaty means that the EU will be able to leave behind 25 years of sterile debates on institutions. The Europeans should now tackle crucial external challenges such as climate change, energy security, migration, nuclear proliferation, the Middle East and Russia.

Blair's leadership could galvanise the union to focus on this outward-looking agenda. He would bring some stardust to an organisation in great need of dynamism and a fresh start. The Lisbon treaty creates a full-time president for the European Council (the regular summits of heads of government), but gives that person no formal powers. His or her influence will depend on their charm, powers of persuasion and force of personality. A successful president will be modest enough not to provoke fears of empire-building among the governments, but strong enough to offer leadership, help to forge a consensus and, when necessary, knock heads together.

Among the 27 governments, there are two theories about what sort of president the EU needs. Nicolas Sarkozy, the French president, wants a big figure with the stature to play a leading role on the world's diplomatic stage. I share that view, but many leaders from smaller member-states want a lesser figure who would not threaten them. They think Blair would be too grand to focus on the details of the business of the European Council.

I am the first to acknowledge that Blair is not an ideal candidate. His support for President George Bush and the invasion of Iraq have made him thoroughly unpopular in many places (I think the Iraq war a huge mistake, but I don't regard Blair as a liar on that issue; the British intelligence services told him that Saddam Hussein had weapons of mass destruction and the intelligence services of our leading allies said the same).

The fact that a lot of people hate Blair could make it harder for him to do a good job as president. If Angela Merkel, the German chancellor, were available, she would be an ideal candidate, being a consensual figure. But she is not and most of the other names touted for the job, such as the prime ministers of Belgium, Holland and Luxembourg, are virtually unknown on other continents.

Blair has clear views on many issues and has therefore made enemies. European federalists scorn him for failing to take Britain into the euro. Protectionists dislike his commitment to free trade. Anti-Americans worry about his belief that Europe should work closely with the US. Furthermore, the European People's party, the centre-right group that is the largest in the European Parliament, is demanding that one of its own should take the presidency (technically, Blair counts as a socialist).

The best argument for a Blair presidency is that it would improve the EU's global credibility. Though the EU makes up 20% of world GDP, it punches below its weight in international diplomacy – because the 27 governments are sometimes divided, but also because its system of external representation is horribly messy.

The rotating presidency, often held by a small country, the commission and the high representative for foreign policy all try to speak for the EU. The Lisbon treaty would scrap the rotating presidency's role in foreign policy, creating not only a full-time president, but also a new foreign policy chief to replace the high representative and the external relations commissioner.

The message I hear in places such as Beijing, Delhi and Washington is that if the EU wants to be taken seriously, it should choose a big name as president. As one Indian official said to me: "If you choose the prime minister of Luxembourg, we may not find time to meet him."

The president will also have a key role to play within the EU. One of the union's biggest problems is that few people understand what it does, how it works or why it contributes to their prosperity and security. Blair is a skilled and effective communicator who could sell the EU to its own citizens.

Another point in Blair's favour is that he made a valuable contribution to the EU during his 10 years in office. In 1998, he had the idea of giving the EU a role in defence policy and that has subsequently led to the deployment of two dozen missions of peacekeepers, policemen and administrators to conflict zones such as Bosnia, Congo, Palestine and the Somali coast. He championed the cause of EU enlargement and, as the Central and East Europeans know, did a lot to ensure that they joined in 2004 and 2007.

During the British presidency in 2005, Blair pushed climate change and energy security to the top of the EU's agenda. The Iraq war certainly prevented Blair from pursuing his ambition of reconciling the British people to the EU. But he is Britain's most pro-European prime minister since Edward Heath.

A President Blair could also help the EU to cope with a Conservative Britain. His presence in Brussels would provoke some Eurosceptics, but if a government led by David Cameron tried to unpick parts of the Lisbon treaty or opt out of some institutions, Blair would be an eloquent defender of the EU on radio and television. He would explain to the British people why Eurosceptic policies could damage Britain's interests.

Yet it may be the Conservatives who spike Blair's chances of getting the job. William Hague, the shadow foreign secretary, has told the other EU governments that the Conservatives would see support for a Blair presidency as a "hostile act". A week ago, Blair was the clear favourite, with the likely support of Britain, France, Germany, Italy and Spain, plus several of the smaller countries. But on my travels around Europe last week, I have found that Hague's comments have made a huge impact.

A number of prime ministers are unwilling to take a step that would incur the wrath of an incoming Conservative government. President Sarkozy and Chancellor Merkel remain supporters of Blair, but are now hesitating over backing a man with so many opponents. The Conservatives may have achieved their first diplomatic coup in Europe, even before taking office.

• Charles Grant is director of the Centre for European Reform

NO. He co-authored the Iraq war and is not a convinced democrat

Although Tony Blair is almost the very last person who should be appointed as Europe's first president, on the face of it he seems the only sensible candidate. At 56 he brims with the energy of a much younger man; he has international standing and experience and an undoubted feel for the needs and ambitions of the big players. By comparison his nearest rival, poor Jean-Claude Juncker, the prime minister of Luxembourg, seems like a harmless worthy who has no better chance in this contest than the mayor of Harrogate.

And if you're half asleep, President Blair sounds sort of convincing, possibly because he has been so long preparing for the role, with a 10-year rehearsal period as prime minister, during which the word "presidential" became shorthand for his dictatorial attitude to parliamentary democracy and cabinet government.

But that is precisely the quality they are looking for to increase Europe's global influence. They want experience of high-altitudes, certainty, drive and L'aerodynamisme; they want Euro-fighter, not Euro-suit. That's because the conclave of European leaders that will elect this new secular pope can ignore public opinion as well as principle in the process created by the Lisbon treaty, Blair's record seems to matter far less than it should. As one commentator said last week: "If the presidency goes to a politician who lacks fame and charisma, its place will forever be low down in the international pecking order."

It is an odd way of looking at a job that gives new and undelineated power to an individual without a mandate of the European people.

If you conceive of a job like this, you surely have higher ambitions than to fill it immediately with a man who was not merely implicated in the decision to go to war in Iraq, but was its co-author.

This love of brand – any damn brand as long as recognition is high – says much about the undemocratic, swooning frivolity of so many European leaders but they may yet come to regret their haste when Blair appears in front of the Chilcot inquiry into the Iraq War. No wonder he pushed so hard to make it secret because, among other things he will shortly be expected to answer questions about the early meetings with George Bush in 2001 and 2002 when the path to war was set, the evidence of distorted intelligence, the pressure on the Attorney General Lord Goldsmith to change his legal advice and the serious accusation that Blair knew of Bush's plan to provoke war by flying U-2 spy planes painted in UN livery into Iraq's airspace.

Something that the European leaders have perhaps failed to grasp is that the central figure of the Chilcot inquiry is Tony Blair and the central issues are whether he took Britain to war in Iraq on evidence which he knew or suspected was false, and whether he sacrificed British national interest, and indeed lives, to the Bush administration's desperate need to go after "something really big" in order to assert American military supremacy after 9/11. Blair's centrality will not vanish when he stops being interviewed by the inquiry and nor will the embarrassment to the European presidency, because it is his judgment and integrity that will be on trial in the first weeks of his presidency, if indeed he is elected for the 30-month term. And when Chilcot reports he will necessarily focus on Blair's premiership, his use or abuse of power.

No doubt this is the argument that the shadow foreign secretary William Hague has been putting to European ambassadors over the last few weeks in an attempt to sabotage Blair's run. But there are others, which Blair's brilliant presentation allow people to forget. The reason he was able commit Britain to war, almost as an act of personal will, is that he has innate contempt for the opinion of others.

He seems to think it is enough for him to utter that oddly childish formulation "I believed I was right at the time", as if believing something right is the same as being right. It allows him not to address his poor judgment and not to make amends, which must surely warn European leaders that his moral/ intellectual equipment is perhaps not all that it should be.

Actually I don't believe that he is without feeling, or conscience, and I am sure he was affected when parents such as Deirdre Gover, who gave such a moving interview to the BBC's Eddie Mair about her 30 year-old son, Kristian, talked of their loss. It must weigh heavily on him.

But let us not forget how thoroughly anti-European his instincts were when he sided completely with Bush and America and paid no attention to Jacques Chirac's opposition, or the millions of sensible people who marched through the capitals of Europe pleading with Bush and Blair to listen to them. That heedlessness should count for a lot now that the Iraq death toll is estimated to be 600,000.

The second part of the argument for disqualification is that Blair is not a convinced democrat, which is important when you realise that Europe is changing with the Lisbon Treaty and acquiring foreign policy institutions and all sorts of shadowy committees to preside over internal security. The new president will be responsible for setting the tone of business at the apex of the EU and ensuring transparency and accountability. Is the man who did so much to undermine the power of the British parliament right for this?

I doubt whether much of this has occurred to European leaders because most leaders appear to be thinking in terms of power and the influence of Europe, not the integrity of its institutions.

When Tony Blair left office in 2007, he seemed to display dissatisfaction with Britain. Although he has homes here, it was if Britain had become too small for him, and very soon he was on the international stage, working as the Quartet Powers representative in the Middle East, trying to repeat his triumph in Northern Ireland, signing up with JP Morgan, speaking, writing, raising money for his religious foundation and teaching at Yale.

He has made a fortune and has kept out of Gordon Brown's hair, but apart from money and tact this astonishing activity seems also to betray an unquenchable ambition.

Who knows? Perhaps it has been since the day he left Number 10. But before European leaders roll over before the charm of this impressive but mysterious man, it is worth their asking whether Deirdre Gover, mother of Kristian, is right when she said: "Tony Blair deceived us on weapons of mass destruction. He should be held responsible for the conflict. He lied to his cabinet, to his government, to parliament and to us."

• Henry Porter writes commentary for the Observer

Three votes for Blair

WILL HUTTON

Tony Blair is a flawed candidate for the EU presidency. He was not a brave pro-European at home. He sided with American neocons. He invaded Iraq. He would inflame British euro-sceptics. But he is the best British candidate. Britain would have an opportunity to lead the EU, and an inside track on trade, security and financial issues. His vision of Europe as a group of nation states finding common cause to advance common interests is realistic. Best to back our man, however imperfect, than refuse a prize that might not come our way again for decades.

Will Hutton is an Observer columnist and executive vice chair of the Work Foundation

ANTHONY SELDON

Tony Blair could be really outstanding. People have him wrong: they think he spent his premiership fixated on Clinton and Bush, but in fact he gave considerable and increasing time to Europe once he had worked out what he wanted to do. His plan to enter the euro was ill-considered, and when Brown defeated it the second time in 2003, he cared little. His defining moment came in Brussels in June 2005, when he set the tone for a more liberal, less bureaucratic and enlarged Europe. Britain needs a voice to match China, India and the US and a Blair is best placed to provide exactly that.

Anthony Seldon is Tony Blair's biographer

COLLEEN GRAFFY

If a poll were taken in the US, both Democrats and Republicans would choose Blair as the clear favourite to lead the EU. Lisbon looks set to launch the European superstate: will it choose to be a partner with the US in tackling global problems or seek a role as a counterweight? Only an Atlanticist president will seek partnership. Only an Atlanticist will work for the EU to have a common defence policy rooted in Nato. Love him or hate him, Tony Blair is an Atlanticist and an international statesman with substance and sizzle.

Colleen Graffy is a former US Assistant secretary of state

Three votes against Blair

PHILIPPE SANDS The president of the European Council must be a person of unimpeachable integrity and judgment, a unifier who can craft consensus at home and inspire respect abroad. Charm isn't enough. In the eyes of many around the world, the Blair government's prosecution of illegal war and possible association with torture make him a most surprising candidate. Europe is entitled to someone who won't be the subject of inquiries. Europe needs a president who is associated with promoting modern values, including the rule of law and fundamental rights for all.

Philippe Sands is a QC and professor of law at University College London

DAVID OWEN

Lord Butler on 22 February 2007 made devastatingly clear why Tony Blair is not a fit and proper person to preside over Council meetings of European heads of government. Butler used the word "disingenuous" to describe how Blair was told by the UK intelligence community "we know little about Iraq's chemical and biological weapons work since late 1988" and yet told parliament just over a month laterthat the picture painted by our intelligence services was "extensive, detailed and authoritative". Like contempt of court, contempt of parliament should always be a disqualification for holding high office. Lord Owen is a former foreign secretary

PIER LUIGI BERSANI

Tony Blair is a personality with a formidable reputation on the European stage who has always enjoyed a very good relationship with Italy. I have always admired him, despite differences over the war in Iraq. However, when it comes to considering him as a candidate for the European presidency, it needs to be underlined that the UK is not in the Schengen Agreement, nor part of the Euro zone and is therefore not central to the process of European integration. Blair is a splendid man but possibly not the right candidate for this job.

Pier Luigi Bersani is a candidate to lead Italy's opposition Democratic Party

LIFE AFTER NO 10

Since leaving office Tony Blair has been busy. Here are a few of the former prime minister's interests.

■ In June 2007 he was offered the role of Middle East peace envoy for the Quartet (the US, EU, Russia and the UN), focusing on working with the Palestinians to improve their economy and build the necessary governance and security in their quest for statehood.

■ In December 2007 he converted to Roman Catholicism and went on to set up the multi-million pound charitable Tony Blair Faith Foundation. It focuses on uniting people of different religious traditions in practical action, for example, the eradication of malaria. As part of this role, he teaches 10 seminars a year at Yale university.

■ In 2007, he set up the Tony Blair Sports Foundation to nurture young sporting talent in deprived areas in the north east. The foundation focuses on indoor rowing, tennis, athletics and football.

■ In January 2008, Tony Blair was given advisory roles with JP Morgan Chase and Zurich Financial Services paying £2m and £500,000 a year respectively.

■ In March 2008, Blair founded the Breaking the Climate Deadlock Initiative. The focus is on countries and regions fundamental to a successful global deal, including the US, the European Union, Japan, India and China.

■ He is a major figure on the lecture circuit, commanding fees of up to £240,000 per 90-minute talk, while his memoirs secured a £4.6m advance from Random House.

■ In February 2009, Tony Blair Associates was set up to provide in partnership with others strategic advice on political and economic trends and governmental reform.

Compiled by Isabelle Chevallot