Prime Minister Theresa May has been told by French president Francois Hollande that Britain needs to trigger Brexit negotiations as soon as it can to avoid the "danger" of uncertainty.

At a joint press conference at the Elysee Palace in Paris, Mr Hollande said it was a case of "the sooner the better" regarding when Britain invoked Article 50 of the Lisbon Treaty, which formally launches Brexit.

READ MORE: Theresa May meets Francois Hollande amid Brexit talks warning

The French president said that he understood London needed time to prepare for the negotiations, but that "uncertainty is the greatest danger".

Mrs May confirmed that the UK would not trigger Article 50 until the end of the year as all sides needed the next six months to formulate their positions.

Mr Hollande made it clear that if Britain wanted to stay in the single market it would have to accept the free movement of labour.

The PM said she expected to be able to guarantee the status of EU nationals in the UK, and the only reason she would not be able to do so would be in the event of the rights of Britons abroad being diluted.

READ MORE: Theresa May meets Francois Hollande amid Brexit talks warning

Mr Hollande said that Britain and France were working together at the UN, in the Middle East, and in dealing with immigration, and he expected that to continue.

The French president said Brexit was the decision of the British people and it needed to be respected.

Mr Hollande's comments came after German chancellor Angela Merkel said Britain should "take a moment" to prepare for withdrawal from the European Union.

Mr Hollande thanked Mrs May for her support in the wake of the Nice terrorist atrocity and insisted it showed the close alliance of the two countries.

READ MORE: Theresa May meets Francois Hollande amid Brexit talks warning