Julian Assange, the founder of WikiLeaks, is today taking his case against extradition to Sweden to the supreme court.

This is his last chance to avoid extradition to face allegations of rape and sexual assault relating to a trip to Sweden in 2010. He denies the claims. In February last year, a court ruled he should be sent to Sweden to answer the accusations against him; he appealed and lost.

The supreme court justices are being asked to rule on the specific question: does a prosecutor have sufficient authority to require someone's extradition? In Britain generally only judges can approve arrest warrants. But the warrant for Assange was issued by Sweden's public prosecutor. Assange's lawyers argue that the Swedish system is unfair because it puts the power to issue arrest warrants in the hands of the same prosecutors who are trying to put him in jail.

As my colleague Esther Addley noted in this very informative piece, many legal observers were surprised when the supreme court not only agreed to hear Assange's petition, but said seven judges rather than the usual five would preside, "given the great public importance of the issue raised".

Julian Knowles QC, a barrister specialising in extradition law based at Matrix Chambers, said the decision to might be more easily explained by the enormous public interest in Assange's case – "to send the message that the highest court in the land has looked at this case, and it's had the attention of the best legal minds in the country".

In Knowles's view, the law in this area – whether a public prosecutor is a valid judicial authority – has been comprehensively tested. "This point has been litigated before, and the courts have always reached the clear answer that while it may look odd to English eyes, common law eyes ... European systems don't have the same structure. The courts have always said that to make extradition work, you have to be flexible in your approach to what extradition is." The consequences if Assange were to win, he said, would be "very profound". "It would basically mean, until the law is rewritten, that extradition to Europe [would] become very difficult, if not impossible. Because in the vast majority of European extradition requests, the arrest warrant is issued not by a court, as it would be in England, but by a prosecutor." It is much easier to predict what will happen if Assange loses. Though he would still have the option to make an application to the European court of human rights (as he has hinted he may do at earlier stages of the process), this would not delay his extradition, since Sweden is also a signatory to that convention.

Assange would probably be kept in custody - bail does not exist in Sweden - and if he is charged a trial might begin in a few months.

The case is set to begin at 10.30am and to last for two days. The judges' decision is then expected in matter of weeks.

Footage of the proceedings will be streamed live here.

(The supreme court has permitted the televising of all its proceedings since it opened two years ago. Adam Wagner has looked at the implications of that here.)

Comments have not been switched on on this blog for legal reasons.

The justices hearing the appeal are: Lord Phillips, Lord Walker, Lady Hale, Lord Brown, Lord Mance, Lord Kerr and Lord Dyson.

Speaking for Julian Assange is Dinah Rose QC, an expert in civil liberties and European Union law.

Speaking for Sweden is Clare Montgomery QC, a specialist in criminal, regulatory and fraud law.

Rose is expected to put her case today for four hours, followed by two and a half hours for Montgomery tomorrow. Rose will then get a one-hour reply.

Phillips, the president of the supreme court, issued guidance in November suggesting that advocates appearing before the court did not have to wear traditional court dress if the court agreed, and neither Rose nor Montgomery will be doing so today. The supreme court justices only wear their robes on ceremonial occasions so will not be wearing traditional court dress either.

Here is an interactive timeline explaining the history leading up to the supreme court's establishment in 2009 and the rulings it has handed down since.

Here is a picture of the supreme court justices when the court was set up. Lord Dyson is not pictured as he had yet to be appointed.

Here are biographies of all the justices.

My colleague Robert Booth is at the supreme court and tweeting events so far.

Julian Assange has arrived smiling and to the sound of I Shall be Released played by a peace activist, Robert reports.

Vaughan Smith, at whose Norfolk home Assange was under house arrest for much of the past year on bail (he moved out shortly before Christmas), slips him a good luck card from his children, Robert writes.

Robert Booth writes from the supreme court:

Julian Assange arrived this morning at the court to a familiar scene - a group of anti-war protestors, free speech campaigners and peace activists coralled behind galvanised zinc barriers. Joined by Kristinn Hrafnsson, his WikiLeaks colleague, he entered the recently restored building to the strains of Bob Dylan's I Shall Be Released, played and sung by a deep-voiced protester. His usual entourage, including Gavin MacFadyen, director of the Centre for Investigative Journalism, and Vaughan Smith, the founder of the Frontline Club for journalists, were waiting. Smith pressed a good luck card written by his children into Assange's hand. Assange had lived with Smith at his home at Ellingham Hall in Norfolk while on bail for a year. The two men hugged.

Julian Assange, his lawyers, the media and others are taking their places at the supreme court now. You can watch proceedings here.

The court rises as the justices file in.

Dinah Rose, speaking for Assange, begins. The question is whether a Swedish prosecutor constitutes a judicial authority under the relevant British act. If not, the warrant is not valid and there is no legal basis for Assange's extradition to Sweden, she says.

Here is the outline of Assange's legal team's case that the supreme court should reject his extradition to Sweden (pdf).

The Swedish prosecutor is a party in the case, so she cannot be a judicial authority, Rose says. That is one of the pillars of natural justice, she says – judicial impartiality and independence.

She says the answer to the question posed by this appeal will require a close examination of the European arrest warrant framework and the way it has been enacted in the UK in the 2003 act.

Rose refers to the case Office of the King's Prosecutor, Brussels v Cando Armas and another. She is running through the history of the European arrest warrant "framework decision" establishing the warrant system. Lord Hope has said this is not an extradition system at all, Rose says. Since the 2003 Extradition Act there are very limited grounds for refusal, she says.

The court media handout sums up the facts of the case like this, Robert Booth tells me:

The appellant, a journalist well known through his operation of WikiLeaks, visited Sweden to give a lecture in August 2010. He had sexual relations with two women. Both women went to the police who treated their visits as the filing of complaints. The appellant was interviewed by police and subsequently left Sweden in ignorance of the fact that a domestic arrest warrant had been issued for him. Proceedings were brought in the Swedish courts in the appellant's absence, although he was represented, in which a domestic warrant for the appellant's detention for interrogation was granted and upheld on appeal. Subsequently, an EAW [European arrest warrant] for the appellant was issued by the Swedish Prosecution Authority that set out allegations of four offences of unlawful coercion and sexual misconduct including rape. The EAW was certified by the UK Serious Organised Crime Agency under the Extradition Act 2003. The appellant surrendered himself for arrest in the UK and, following an extradition hearing, his extradition to Sweden was ordered. The order was upheld on appeal to the divisional court.

Rose now refers to the case of Dabas v High Court of Justice, Madrid. In reference to this case, Lord Hope said complexity and delay were inimical to the objectives of the extradition warrant system, Rose says.

Rose is making the point that Lord Bingham has said the system depends on mutual recognition of judicial systems and the UK should defer to the foreign judge on matters of their own judicial system. That system is undermined if arrest warrants are administered by a prosecutor, not a judge, Rose says.

Rose now turns to the proper interpretation of the European arrest warrant framework - the context, the legislative decision, and the language.

She looks first at the context. Before the current agreement, extradition was governed by bilateral decisions and a 1957 European convention. This was a system of agreements between states, not of backing warrants.

The convention refers to the "competent authorities" in each country.

Rose compares the wording of the 1957 convention and associated documents in English and French, reading out a few lines from the French version in French. The French version says "judicial authorities" not "competent authorities" and seems to include the prosecutor.

The prosecutor in France has a role in the judiciary, Lord Phillips, the president of the supreme court, points out. Rose says that is absolutely right and she will return to that.

It was understood at the time that only a person independent of the executive and both parties can fulfil the function of judicial authorities, Rose says.

Rose is now reading out the passages relevant to extradition from the European convention on human rights, and comparing the English and French wording. The wording has been carried over to the European arrest warrant framework decision, she says.

She is trying to establish that the judicial authority referred to is "a judge or other officer authorised by law to exercise judicial power".

Swedish prosecutors cannot exercise this kind of judicial authority, Rose says, because they are not independent.

Rose turns to the Schiesser v Switzerland case. The court found that there were limits to the inclusion of prosecutors in the definition of judicial authorities if the prosecutor was not independent, Rose says.

Rose now turns to Skoogstrom v Sweden (1984), a decision of the European commission on human rights, in which, she says, it was expressly held that a Swedish prosecutor could not be "a judge or other officer authorised by law to exercise judicial power" for the purpose of Article 5(3) of the European convention on human rights, because she lacked the essential quality of independence.

Montgomery's case, for Sweden, gives no definition of judicial authority, Rose says.

The most recent relevant European court of human rights decision is Medvedyev v France, Rose says. In this decision the court held that the investigating magistrate fulfilled the role of a "judge or other officer authorised by law to exercise judicial power".

Rose turns to the European council meeting in Tampere, Finland, in 1999 creating an area of freedom, security and justice in the European Union.

The aim was to get to the point where EU states recognised each other's judicial systems with the minimum of formalities.

The issue of public acceptance in one country of another's judicial system was discussed at the time.

Asked about a seemingly restricted document she is referring to, Rose says: "It would be better to see more things. Better not go there today," she adds, to laughter from the court.

In 1999 the UK drew the attention of the rest of the EU to the Backing of Warrants (Republic of Ireland) Act 1965, which says a warrant should be issued by a "judicial authority" - "a court, judge, justice of a court, or peace commissioner". A peace commissioner is an honorary official whose functions consist of issuing this type of document, she says.

"It is immediately noticeable that that list does not include prosecutors or anyone who is not independent," Rose says.

"That was the model that the UK delegation" set out to the other EU countries, she says.

In September 2001, following the 9/11 attacks, the European commission proposed a new arrest warrant framework.

An explanatory memo with this draft framework made the same reference to "judicial authority", here explicitly defining that as "judge or public prosecutor". This is based on mutual recognition of court judgments. State to state relations on extradition are replaced by court to court relations, she says.

That proposal was not agreed by member states. The proposal that was agreed was significantly different, she says.

A second draft was produced, she says, in December 2001. The definition of judicial authority has gone from this draft and does not appear in the final version eventually approved, Rose says.

Instead the draft says the European arrest warrant shall be a court decision by a member state. It is no longer a request, it is a court decision.

The justices point out that in the final version this becomes "judicial decision" - not including the public prosecutor. Rose gets a bit annoyed that everyone is jumping ahead.

"This legislative history supports us, because it indicates that the member states rejected this wording [ie rejected the specific inclusion of the public prosecutor as part of a "judicial authority"]," she says.

The judges (all of whom, except Lord Dyson, are peers) complain that Rose is now referring to House of Commons committee findings, rather than those from the House of Lords, which they say is generally accepted to be of higher quality. Rose apologises but says "we will have to make do with the other place".

The Commons European scrutiny committee said in 2002 "we think it regrettable that the term 'judicial authority' is not defined" in the European arrest warrant framework decision, Rose points out.

The European commission subsequently proposed a European public prosecutor - a proposal that never came to fruition. The prosecutor would have had to have applied to a court in a member state to get an arrest warrant issued. So the proposals show that an arrest warrant decision must be made by a court, not a prosecutor, Rose says.

The wording of the final EU framework on extradition is that the European arrest warrant is a "judicial decision", Rose points out.

It goes on:

The issuing judicial authority shall be the judicial authority of the issuing member state which is competent to issue a European arrest warrant by virtue of the law of that state.



When the framework was incorporated into British law as the Extradition Act 2003 the phrase:

A Part 1 warrant is an arrest warrant which is issued by an authority of a category 1 territory ...

in the draft extradition bill was changed to:

A Part 1 warrant is an arrest warrant which is issued by a judicial authority of a category 1 territory ...

in the final act.

The Commons home affairs select committee said the reference to judicial authorities should mean judicial authorities that operate in an "independent manner", Rose says.

Rose criticises the high court for basing its judgment on drafts that said the public prosecutor could be part of a judicial authority, when that was dropped from the final legislation.

Rose sums up what she has been saying so far today:

When one looks not only at the context in which the framework decision was made and the way that legislation evolves ... there is a very strong indication that the intention was as a safeguard ... that the warrant should be issued by a judicial authority acting independently and exercising recognisable judicial functions.

That was a concern of the UK parliament and the EU council of ministers, she says.

Rose now turns to the language of the European arrest warrant (EAW) framework. This can only be understood as referring to a judge, she says.

It cannot be construed in the way Montgomery, for Sweden, wants to present it.

The final EAW framework agreement uses the word judicial "over and over again", Rose says.

"It is simply not possible to conclude" that the issuing judicial authority could include a public prosecutor but an executing judicial authority could only be a judge, Rose says.

And with that they break for lunch.

Here is a summary of today's key events so far.

• It's been a morning of dense legal argument at the supreme court about the nature and provisions of the European arrest warrant system. Dinah Rose, Julian Assange's QC, is attempting to argue that because in Sweden a prosecutor requests an arrest warrant rather than a judge, that makes the warrant invalid.

• Rose has taken the justices back to the 1957 European convention on extradition, which preceded today's extradition framework, and the decisions that led up to the creation of the European arrest warrant framework and its incorporation into British law as the Extradition Act 2003. At each stage, she says it is clear that the intention was that a judge - or at least someone independent of both parties, ie not a prosecutor - would be the one to ask for extradition.

• Rose is working hard to back up her case. But it is unclear at this stage if her arguments can get past the fact that the UK, through the European arrest warrant framework, does have an extradition agreement with Sweden, and has therefore already implicitly agreed to respect the way Sweden issues warrants for extradition.

Dinah Rose, Julian Assange's QC, has resumed her argument.

If a non-judicial authority (for example a prosecutor) requests an arrest warrant, there is no compulsion under the European arrest warrant framework for another state to recognise it, Rose says.

Rose says some states have approached the question of what is and is not a judicial authority with "extraordinary vagueness and casualness".

Sweden has listed its national police board as a judicial authority, Rose says; some other EU countries list judges, and others prosecutors. "Quite a number who have designated prosecutors have also designated judges," one of the justices points out. Rose agrees.

She directs the justices to the European commission's report of 2009 evaluating EU countries' evaluations of the arrest warrant system. The report said:

In some member states non-judicial authorities continue to play a role … This seems difficult to reconcile with the letter or the spirit of the system.

It called on those member states which had not done so to remove non-judicial authorities play from this system - referring to Ministries of Justice rather than prosecutors, she says.

Lord Brown says Rose admits that the term judicial authority is capable of being more widely interpreted, as she has pointed out that the Irish have done exactly this. "My lord, no," says Rose. The UK was not prepared to give this term such an extended meaning, she says. "What is striking is the difference between the 2003 act in the UK and the 2003 act in the Republic of Ireland," Rose says. "You have to look at what the framework decision requires and not what it permits." The UK implemented it in a minimal way - unlike Ireland, she says.

Swedish public prosecutors have very wide powers, Rose says. The Swedish national police board, which Sweden lists as a judicial authority, could never be considered a judicial authority under the EAW framework, she says, so "on any view Sweden has failed properly to implement the framework decision - the question is: how badly?"

Rose turns to what she calls the flaws in the divisional court's earlier decision on Assange's extradition, and the divisional court's claim that the words judicial authority have two separate meanings

The French public prosecuting system does not "fall foul of independence", Rose says. The Swedish one, by contrast, is "a common or garden prosecutor".

Rose admits there is a decent degree of independence of the Swedish public prosecutor from the executive, but is a "party" in criminal cases. "Independent of government, but it's a party," says Lord Brown. European institutions have defined it this way, Rose says.

"Is it proportionate to require this man's extradition?" asks Rose, referring to Assange. He has not been charged, he is offering to be interviewed by video-conference, he would have to leave his home, she says.

The Swedish prosecutor has an interest in whether he is extradited, says Rose. How can the prosecutor make an impartial decision about that, she asks.

This is not a valid part one warrant, Rose says. It's not in accordance with the usual safeguards the UK would demand.

The divisional court asked for more scrutiny, but Lord Kerr says he cannot think what that might mean. Rose agrees.

With that she finishes her submission to appeal.

Clare Montgomery, for Sweden, begins by taking issue with Rose's contention that the Swedish prosecutor cannot be impartial.

In this case, there is no need to adjudicate between two separate parties, Montgomery says, because the question is only: should Assange be extradited?

That is necessarily a decision, and adjudication, that will be made throughout Europe by a party, whether it is a public prosecutor or a policeman.

The justices question this. Montgomery goes on:

The decision whether to arrest somebody is normally made by someone who might be regarded as being partisan.

Lord Brown says they are not talking about arrest, but extradition.

In any case where a public prosecutor plays this role, a judicial decision will have preceded it, Montgomery says. Fundamental rights are protected, she says.

"The core decision is normally taken by someone who is a party," Montgomery says.

"Not in this country," interrupts one of the justices.

It requires a decision by a prosecutor or the police to set the matter in train, she says.

"But here you have the perceived added safeguard of going to a court," Lord Kerr says.

It is very difficult to take the English or Irish experience and say it should be rolled out to all other EU countries, Montgomery says.

Lady Hale begins a question with: "Supposing Miss Rose is right in her argument, which I'm not for a moment suggesting, but for the purposes of this question..."

Montgomery says she fully accepts the idea that the term "judicial authority" means two different things within the EAW framework decision agreement, an idea Rose had found untenable.

Lord Mance takes issue with Montgomery's assertion that if they rule in favour of Assange they would be taking a narrower view of the EAW framework decision.

Montgomery is coming under more hostile questioning than Rose did.

Montgomery says:

The term judicial authority was chosen for its extended continental autonomous meaning, namely those authorities who under the constitutions of their various countries could properly be regarded as judicial authorities.

At that point, the supreme court adjourns until tomorrow.

Here is a summary of today's key events so far.

• It's been a day of dense legal argument at the supreme court about the nature and provisions of the European arrest warrant system. Dinah Rose, Julian Assange's QC, attempted to argue that because in Sweden a prosecutor requests an arrest warrant rather than a judge, that made the warrant Sweden issued against Assange invalid.

• Rose took the justices back to the 1957 European convention on extradition, which preceded today's extradition framework, and the decisions that led up to the creation of the European arrest warrant framework and its incorporation into British law as the Extradition Act 2003. At each stage, she said it was clear that the intention was that a judge - or at least someone independent of both parties, ie not a prosecutor - would be the one to ask for extradition.

• Clare Montgomery, speaking for Sweden, took issue with Rose's claims that the Swedish prosecutor could not be impartial. In the Assange case, the prosecutor was not adjudicating between two parties, so that problem did not arise. In Britain a case is instigated by a prosecutor or the police too, she said. And the drafters of the European arrest warrant agreement always intended the term "judicial authorities" to include prosecutors in many countries, she claimed.

• Montgomery gave a much less confident performance than Rose, and came under harsher questioning from the justices. But it is unclear at this stage if Rose's arguments can get past the fact that the UK, through the European arrest warrant framework, does have an extradition agreement with Sweden, and has therefore already implicitly agreed to respect the way Sweden issues warrants for extradition.

• The case continues tomorrow with more from Montgomery, followed by a reply from Rose. The justices are likely to take a few weeks to hand down their decision.