In response to a question from Ms Harman, the PM gives a guarantee that any children who are given refuge under the scheme will not be at risk of forced deportation when they turn 18. Ms Harman welcomes this and goes on to praise the efforts of the Royal Navy in rescuing people who have become stranded on the Mediterranean. Mr Cameron says that 6,500 have been rescued in this way, but insists that the international community must "break the link" between those getting on boats and the possibility of resettlement in Europe.

The exchanges, as predicted, are relatively low-key so far. Mr Cameron talks about the support that the UK is giving to Syria, "playing its role" by funding refugee camps and meeting the 0.7% international aid pledge. As for giving refuge to unaccompanied children, the PM says he will listen to Save The Children and others but he is also conscious of the dangers of separating children from their family. Ms Harman urges the PM to come back to the Commons with more details over the next month.

The prime minister says there is no limit on the number of refugees who will be accepted this year, insisting "let's get on with it" and do everything possible to help people and give them a "warm welcome" But Ms Harman presses for further reassurances on this and asks why the PM has ruled out accepting people already in Europe, urging him to reconsider. 

Before David Cameron responds, her pays tribute to Harriet Harman at her last PMQs, saying that she has been a "robust adversary" in the Commons and a "fierce champion" for her constituents. 

Harriet Harman is on her feet. She gets a loud cheer from all sides of the Commons. She goes, as expected, on the refugee crisis, saying it is the "largest movement of people across Europe" since 1945. She asks about the 20,000 people the UK pledges to accept over the next 5 years, adding that this must be "seen as lifetime away". 

David Cameron is on his feet in the Commons. The first question is from Tory MP Julian Knight about education in his Solihull constituency. The PM replies by banging the drum for free schools, saying they bring more "good and outstanding" school places.

The BBC's political editor Laura Kuenssberg tells Daily Politics that there will be a "lot of warmth" for Ms Harman and she is expected to strike a serious note by asking about the refugee crisis. Because of events in the last week, it could be quite a low-key occasion with few fireworks ahead of the "real event" next week, she adds. 

With less than five minutes to go, the Commons is pretty much already full. The session to mark the Queen becoming the UK's longest-serving monarch has been very well attended. 

This is the first PMQs for more than six weeks so here's a bit of a reminder about the protocol. Opposition leader Harriet Harman will get six questions while the SNP's leader in the Commons Angus Robertson will have two. Other MPs scheduled to ask questions include former Green Party leader Caroline Lucas and veteran Conservative Sir Peter Bottomley. 

House of Commons
Parliament

Leader of the Opposition Harriet Harman follows the prime minister in paying tribute to the Queen and the length of her reign. 

Ms Harman says "Her life has been a great sweep of British history and it is no exaggeration to say that she is admired by billions of people around the world".

The acting Labour leader causes amusement in the chamber by remarking that Her Majesty is now on her twelfth prime minister "although we on these benches had hoped she would now be on her thirteenth". 

Ms Harman provokes another burst of laughter when she says "the Queen reigns over 140 million people - that's nearly as many as the number of the Labour Party's registered supporters".

Chuka Umunna says there has been a "degree of entryism" in the Labour leadership election but that, in general, the large number of people who have joined the party since 2010 should be welcomed. While there has been "an explosion of debate" during the contest, he says some of the criticism levelled at candidates such as Liz Kendall, has been "extremely distasteful". He calls for more internal debate in the party but regrets that details of his new campaign group - Labour for the Common Good - had been leaked to the media, saying it was wrong to characterise it as a forum for opposition to Mr Corbyn.

House of Commons
Parliament

David Cameron leads the speeches marking the Queen becoming the longest serving monarch. The prime minister says that it is "typical of her selfless sense of service" that the Queen has insisted today be treated as any other.

Mr Cameron says "while I rarely advocate disobeying her majesty, least of all in her own parliament, we should take a moment as a nation to mark this historic milestone". The prime minister says the country should thank her majesty for the "extraordinary service she has given our country for over 60 years".

The Daily Politics

Chuka Umunna says the Labour leadership election is "hard to predict" because of the new system being used. He tells Daily Politics that everyone should rally behind the new leader, whoever that is, saying that although Labour is a "broad church" everyone in the party shares the same principles. Whether he remains in the shadow cabinet or not - and he suggests he would not do so if Jeremy Corbyn wins - the shadow business secretary say he will give his backing to whoever he wins. 

Image source, PA

We've been doing our sums here and we think this is Harriet Harman's 35th and last appearance at PMQs. The first was in April 2008, when she deputised for Gordon Brown when he was in Russia. On that occasion, she asked about the state of the UK economy and events in Zimbabwe. Over the past seven years, she has faced David Cameron 16 times, William Hague 12 and Nick Clegg seven. She is likely to get a warm reception on both sides of the House at her valedictory appearance but will she, as they say in the theatre, leave them wanting more...

House of Commons
Parliament

The House of Commons kicks off today at 11.30am with the usual half hour question session being postponed to allow MPs to mark the occasion of Queen Elizabeth becoming our longest serving monarch.

Prime minister's questions follows, as usual, at noon.

This is the last PMQs of an era at Westminster, as Harriet Harman takes her bow. She has appeared in various guises at the weekly exchanges, both as deputy Labour leader and acting leader, since 2007, facing variously David Cameron, William Hague and Nick Clegg across the despatch box. On Saturday, she will stand down from the Labour frontbench, where she has served pretty much continuously since 1982. Expect David Cameron to pay tribute to Ms Harman's long record of service to her party and country, perhaps with an odd joke thrown in at the expense of her possible successor.