Image source, Reuters

Arriving at the summit, German Chancellor Angela Merkel tells journalists the PM's request for an extension should be discussed "openly and constructively".

"The greatest interest for us is an orderly withdrawal of the UK from the EU and to maintain the unity of the 27," she says.

Mrs Merkel adds she has "no doubt" that EU leaders will achieve unity over the extension request.

She says it is "very important" that any extension involves the UK making preparations to take part in the European Parliament elections from May.

BBC News Channel

The BBC's Europe Editor Katya Adler says "don't take anything for granted" on whether or not an extension will be granted, but it is unlikely that the EU would not extend Article 50 again.

"All of them want to avoid a no-deal Brexit," she says.

The EU wants to introduce a longer delay to make sure that there aren't emergency summits "every two weeks" to keep allowing short extensions to the process, she adds.

"EU leaders are wary, they've been watching Parliament for very long, they know the ongoing divisions," she says.

Image source, EBS

Irish PM Leo Varadkar says he is "very confident" an extension will be agreed - but the length and the conditions attached are "still open".

He says the UK is in a "difficult position", and "maybe half the population don't want to leave".

He says he has an open mind as to the length of any extension, but EU leaders will want to hear from Theresa May "what the plan is".

Mr Varadkar says he would like the EU to consider the possibility of a customs union with the UK, and be "generous" in ensuring the UK is not a "silent partner" and would have a "say in decisions being made".

Image source, Reuters

Speaking to reporters, French President Emmanuel Macron says "nothing should be taken for granted".

He says nothing was certain on a Brexit decision, and now was the time for the UK to make a choice.

The EU needed to be certain why the UK should get more time, he adds.

The EU project "must continue" despite Brexit, he says, warning that its unity is still at risk and "nothing must compromise it".

Image source, EBS

Also spotted heading into the building - Danish PM Lars Lokke Rasmussen, Sweden's Stefan Lofven, and Estonia's Juri Ratas.

Image source, EBS

Latvia's Krisjanis Karins says it is "up to the Brits to decide" what happens next.

The options include a no-deal Brexit, leaving under the terms of the current Brexit deal, or revoking Article 50 and cancelling Brexit.

The EU he says, should not "say no" to the UK if it needs more time. "If they need a little more time, I think it's reasonable to discuss", he adds.

Pressed on whether he would favour a long extension, he says: "let's see".

Image source, EBS

Also arriving at the summit is Czech PM Andrej Babis, who tells reporters outside that he hopes for a shorter meeting than last time.

He says it is difficult to predict what will happen tonight, but he hopes an agreement can be found to give the UK "much more time than expected".

He says the condition that the UK begins to organise European Parliament elections is "very important for us".

He says for his part, a delay to Brexit until the end of next year would be "fine".

BBC News Channel

Conservative Sir Bill Cash says that if the EU places conditions on the UK remaining longer in the EU, then it is "unlawful".

He says if there is another extension to Brexit of another year then there is another £12bn being paid to the EU.

On the prime minister delaying Brexit for a second time, he says "we see another broken promise" from Theresa May on Brexit.

The veteran Eurosceptic MP earlier revealed he has written to European Council president Donald Tusk warning that an extended delay was likely to be challenged in the British courts.

We've had a steady trickle of EU leaders arrive at the Europa building in Brussels ahead of the summit this evening.

Hungarian PM Viktor Orban, Maltese PM Joseph Muscat and Slovakia's relatively new leader Peter Pellegrini have all gone inside.

BBC News Channel

Eszter Zalan, from the EUObserver, says that the EU Council is looking at the best way to put pressure on the UK to agree the withdrawal agreement.

"The core of the debate" tonight is whether it should be a short or long extension, she says.

Member states will be seeking a "strong political commitment" that the UK should not try to disrupt the work of the EU too much.

Image source, EBS

Theresa May has arrived in Brussels, telling reporters that she "regrets" the need for the emergency summit because the UK "should have left the EU by now".

Talks between the government and Labour have been "serious and constructive", she says, but the UK needs "extra time" to ensure it can leave in a "smooth and orderly way".

The important thing, she says, is that any extension to Article 50 allows the UK to leave the EU "at the point at which we ratify the deal".

"That would enable us to leave by the 22 May," she adds.

Theresa May has arrived at the EU leaders' summit in Brussels.

The prime minister addressed reporters, ahead of meeting EU leaders and Council president Donald Tusk.

House of Commons
Parliament

Image source, MoD/Crown Copyright

The Commons has now moved on to a general debate to mark 50 years of the continuous at sea deterrent.

The continuous at sea deterrent is also referred to as "Operation Relentless".

The government says that the deterrent is "the minimal, credible and independent deterrent against aggression towards the United Kingdom".

Four submarines guarantee that there is always at least one deployed operationally at any given time.

The first of the four Vanguard Class submarines became operational from 1992.

They are due to continue serving until the 2030s and carry the Trident strategic nuclear armed missile system

House of Commons
Parliament

MPs are now taking part in a debate on a statutory instrument relating to renewable energy in Scotland.

This debate may last up to 90 minutes.

House of Commons
Parliament

Labour's Louise Haigh introduces a bill under the ten minute rule.

The bill intends to strengthen rights for victims of rape and domestic abuse in family courts.

Ten minute rule bills are introduced by individual MPs, and are unlikely to progress without government support.

House of Commons
Parliament

Image source, Press Association

The Commons is now hearing a question on voter ID pilots taking place in the UK.

Next month, 10 local authorities will trial voter ID in local elections.

At least 350 citizens last year were unable to vote when they had previously voted all their lives, says shadow voter engagement minister Cat Smith.

Braintree, Broxtowe, Craven, Derby City, Mid-Sussex, North Kesteven, North West Leicestershire, Pendle, Watford and Woking are all taking part in trials this year.

The first minister of Wales will request Welsh Assembly members be recalled from recess if the summit in Brussels later today results in the the UK leaving the EU without a deal.

Writing to Presiding Officer Elin Jones, Mark Drakeford said such an outcome is "unlikely" but added if there were a recall, assembly members could sit on Thursday afternoon.

This would allow the Welsh cabinet to meet in the morning.

Read more here.

BBC Politics Live
BBC2's lunchtime political programme

Conservative ministers are now openly discussing who could replace Mrs May as PM: