Addressing MPs, Cameron said he had no doubt that "difficult economic times" lay ahead for the country, and that securing access to the single European market was the most important issue for a post-referendum UK.  Speaking the day after he dined with European leaders for a "last supper" in Brussels -- and as those leaders met again Wednesday without him to discuss the post-Brexit future -- Cameron had a clear message from EU heads: that access to the European single market will not be granted without some tradeoff regarding the free movement of people across borders.  "This issue of immigration versus the single market... this is frankly the biggest and most difficult issue to deal with," said Cameron.  Following two days of meetings on the Brexit, the leaders of the 27 other EU countries released a statement underlining that the UK had to accept the free movement of people to retain access to the single market.  "Leaders made it crystal clear today that access to the single market requires acceptance of all four freedoms, including the freedom of movement," said Donald Tusk, president of the European Council.  "There will be no single market a la carte."  At a news conference following the meeting, Tusk said he accepted the need to strengthen controls on Europe's external borders in response to the migrant crisis, following a referendum campaign in which immigration was a core issue.  "It was also a very clear message from David Cameron's side, but also today during our discussion among (EU) leaders... that irregular migration was -- and is -- one of the most important reasons of this crisis of self-confidence in Europe."  The parliamentary session in London also saw fiery clashes between Cameron and opposition leader Jeremy Corbyn, who is refusing to resign in the face of a revolt from members of his own party, as the repercussions from the Leave vote continue to unfold.  Corbyn overwhelmingly lost a no-confidence vote by Labour MPs Tuesday amid criticisms he was lackluster in his campaign to keep Britain in the EU.  Facing questions from Corbyn, Cameron responded that he should step down "in the national interest."  "It might be in my party's interest for him to sit there. It's not in the national interest, and I would say, for heaven's sake man, go."  Tuesday's no-confidence vote against Corbyn was non-binding, but it paves the way for an official leadership challenge.  In response to a question from Corbyn about increased xenophobic attacks in Britain following the Leave vote, Cameron said the government would soon be publishing a new action plan on hate crime, and called on MPs to condemn the attacks.  "That's not what we do in Britain," he said.  While Cameron has returned from the corridors of European power, Scottish First Minister Nicola Sturgeon is in Brussels Wednesday to court European leaders over ways Scotland could potentially remain in the EU.  "I have set out very clearly Scotland's desire to protect her relationship with the European Union," she said, following a meeting with President of the European Parliament Martin Schulz.  "I don't want to underestimate the challenges that lie ahead for us in seeking to find a path. This is very much an initial meeting of a series of meetings in Brussels today so that people understand that Scotland, unlike other parts of the United Kingdom, does not want to leave the European Union."  Scotland, one of the countries that makes up the United Kingdom, voted by 62% to stay in the EU, but its voters face being removed from the bloc due to the Leave vote across the whole of the UK.  Sturgeon, who is meeting key EU figures including European Commission President Jean-Claude Juncker, told the devolved Scottish Parliament Tuesday that "everything must be on the table to protect our place in Europe" -- including a potential second referendum on independence from the UK.  Scotland voted by 55% to remain in the UK in a 2014 referendum, but the Leave vote meant there had been "a very real and material change to Scotland's circumstances," she said.  "The country and the constitutional settlement the people voted for in 2014 is no longer a reality," she said.  Besides fueling renewed talk of Scottish independence, Britain's shock vote last week to pull out of the EU has wounded the European project, sent the pound tumbling, hurt global markets and left a gaping leadership vacuum in the UK.  The divorce itself is shaping up as a messy undertaking, with Europe and Britain at loggerheads on how to even begin the complicated disentanglement after more than four decades together.  Cameron wants to hold off invoking Article 50 of the Lisbon Treaty -- which will officially begin the separation process -- until a new leadership is in place, with a vision on what a future deal with the European Union will look like.  Europe is refusing to engage in talks, formal or informal, until Article 50 is triggered.  Cameron outlined his position to the House of Commons Wednesday.  "They have said no negotiation without notification. But I don't think that excludes discussion that a new prime minister can have with partners, or indeed with the institutions, so that we continue to get off on the right foot."  At the conclusion of Tuesday night's meeting, Tusk said EU leaders understood "that some time is now needed to allow the dust to settle in the UK."  "But they also expect the intentions of the UK government to be specified as soon as possible," he said.  But at this critical juncture in its history, Britain is looking effectively leaderless.  The 52% vote to leave Europe has sent shockwaves through the UK's political establishment, leaving the leadership of both major parties up for grabs.  Candidates from the ruling Conservative Party are jockeying to replace Cameron following his announcement of his intention to resign in the wake of his referendum defeat.  Prominent Leave campaigner Boris Johnson and Cameron ally Theresa May are seen as front-runners, while work and pensions secretary Stephen Crabb has also declared his intention to run. Education secretary Nicky Morgan and health secretary Jeremy Hunt have also said they are mulling a bid.  A successor is not expected to be announced until early September.  - / 382 districts reporting  - / - districts reporting  Meanwhile, Corbyn has refused to stand aside in the face of a revolt from his MPs. Angela Eagle, one of the prominent Labour MPs who resigned from Corbyn's leadership group in recent days, is seen as a leading contender to replace him, along with Labour's deputy leader Tom Watson.  Corbyn, an MP since 1983, comes from the hard left faction of the center-left Labour Party.  While he attracted tens of thousands of new members when he become Labour leader in September, he has been a polarizing figure.  CNN's Elizabeth Joseph and journalist Simon Cullen contributed to this report.
Outgoing British Prime Minister David Cameron faced Parliament Wednesday for the first time since Britain's vote to leave the EU, delivering a stark message from Brussels on the challenges ahead for the UK.