U.K. Prime Minister, David Cameron | Dan Kitwood/Getty Images David Cameron: We won’t trigger Article 50 now British PM tells parliament that when to trigger negotiations is a ‘sovereign decision’ for the UK alone.

Prime Minister David Cameron told parliament on Monday that Britain will not launch formal proceedings to leave the European Union “at this stage,” calling it a “sovereign decision” for Britain to take.

The Conservative leader, who announced after last week’s vote to leave the EU that he would step down as prime minister by October, said he had spoken with European leaders including Germany's Angela Merkel and France François Hollande in recent days about the need to prepare negotiations for Britain's departure.

Leading Brexit campaigners, including Cameron's potential successor Boris Johnson, have said they would like informal talks to start before they launch the formal process. But a German government spokesman said on Monday that Merkel rules out any informal talks with the U.K. about its future relations with the EU until London starts the formal process to leave.

Cameron said his discussions with the German and French leaders focused in particular on "the fact that the British government will not be triggering Article 50 at this stage," said Cameron, referring to the article in the Lisbon Treaty that member countries must invoke in order to leave the EU.

Triggering Article 50 "is clearly what our partners want us to do, although not all of them believe that we have to do it immediately," the prime minister said. "That is why I think we have some time to examine the right model we want to negotiate for and then pull that trigger.”

"We need to determine what kind of relationship we want with the EU, and that is rightly something for the next prime minister and their cabinet to decide," said Cameron. “This is our sovereign decision and it will be for Britain, and Britain alone, to decide.”

He added: “I think it’s right not to trigger Article 50 because that starts a process that within two years has to result in an exit and it might be an unmanaged exit if it started too soon.”

Cameron, facing parliament for the first time since the Brexit vote and the announcement of his resignation, said his cabinet had decided to set up a new "EU unit" from various government departments to negotiate Britain's exit. He described this unit's work as "the most complex and most important task the British civil service has undertaken in decades."

Britain's main interest in such talks will be to maintain access to the EU single market, although from the point of view of some remaining EU member countries, that access would require U.K. acceptance of EU rules about free movement within the bloc.

“There is obviously a very strong case for trying to remain in [the] single market in some form, but that is going to be a decision for the new government and for the parliament,” said Cameron.

He also paid tribute to Jonathan Hill, Britain’s outgoing European commissioner for financial services, who announced his resignation Saturday.

“I’m very sad to see him go," Cameron said. "I think we should try to seek a replacement because the fact is we are a full member of this organization, a contributing member, a paying member until we leave, and so therefore we should have a commissioner, but I’m sure that will be a challenge.”