LONDON: David Cameron says Britain "will not and should not" turn its back on Europe as it leaves the European Union.

After discussing the vote to leave with other EU leaders, he said trade and security co-operation would be vital whatever the shape of future links.

But he said immigration was a "great concern" among UK voters and squaring this with access to the EU single market would be a "huge challenge".

Germany's Angela Merkel said the EU must "respect the result" of the vote.

But German politicians have insisted the UK cannot "cherry-pick" aspects of the EU.

Earlier on Tuesday, Chancellor Merkel said the UK must accept free movement if it wanted to retain access to the single market.

Merkel said the Brexit vote had been discussed "very intensively and deeply" at the dinner meeting with EU leaders.

"We all regretted the result and made clear that the legal procedure must be that the UK invokes Article 50.

"Mr Cameron said he would hand it over to the new government to do... we all agreed that before that point, there can be no formal or informal negotiations."

Merkel said Mr Cameron expressed how he had expected a different result in the referendum, but she added that "We are politicians; we can't spend a long time mourning".

She also said that "Publicly... we can see no way to turn this around. It's not a time for wishful thinking, but of contemplating the reality."

She added that talks would be "on the basis that we expect the representative of the UK to say what idea he has about withdrawing from the EU".

"The request to withdraw will say what sort of relationship the UK wants. But there can be no quasi-negotiations."