There was a strangely jolly, almost flirtatious mood at Prime Minister's Questions today, as David Cameron paid tribute to Harriet Harman as a "credit" to her party. Facing Harman for the last time before the Opposition elects a new leader, Cameron joked that Labour's acting leader was the "most popular" of the three Labour leaders he has faced including Tony Blair and Gordon Brown. And he reminded the House that "it's au revoir" rather than "goodbye" as Harman remains elected as deputy leader, a role in which may well see her stand in at the despatch box in the future.

Harman expressed sympathy to Cameron over the death of his father, and congratulations over the birth of his new daughter, but asked some tough questions on human trafficking. Harman urged Cameron to opt in to an EU Directive on the issue, but Cameron refused, claiming it goes no further than the Government's own plans. Harman said "I know some in his party are irrationally hostile to Europe" but that she hoped Cameron would not let them get in the way of signing up to the EU Directive. Cameron later implied he would consider arguments from Labour MPs for signing up to the directive.

In a separate and more partisan exchange, Cameron said it was "the height of irresponsibility" for shadow ministers to go to the TUC and encourage strikes amid the need for cutting the budget deficit.

Finally, Harman asked Cameron if the Tories were still enthusiastic about returning PMQs to twice a week, as they sometimes argued while in Opposition. Unsurprisingly, Cameron said he favoured a once a week session, describing that as "one of the few things" with which he fully agreed with Tony Blair.

UPDATE: The Prime Minister is wrong to say that Britain does not need to sign the EU Sex Slave Trafficking Directive, says former Europe minister, Denis MacShane, secretary of the All Party Parliamentary Group on Trafficking.

"Last week Teresa May told me Britain would not opt in. Today the PM said he would examine the issue but claimed British laws covered all the problems. But the whole point of an EU directive is that it obliges cross-frontier cooperation and an obligation meet EU rules.

"Sex slave trafficking cannot be combatted on a nation-only basis. The Government is sending out the wrong signal by saying No to a European-wide coordinated campaign. It was sad to see Nick Clegg whispering in David Cameron's ear to provide arguments for traditional Tory Euroscepticism on EU directives.

"The campaign against sex slave trafficking will continue and many will be disappointed at the opposition of Mr Cameron to this important EU directive," MacShane added.