EU leaders on Friday agreed to open the next stage of Brexit talks but laid down conditions for what is expected to be a tough phase of negotiations.

Here are the key elements of the EU's nine-point set of guidelines:

- Make phase one real -

The agreement tells EU Brexit negotiator Michel Barnier to move on to the next phase of talks but warns that the commitments agreed last week must be "respected in full and translated faithfully into legal terms".

The EU voiced concern about possible British backsliding on the hard-fought deal on the first stage, after Brexit minister David Davis suggested it was not legally enforceable.

- Transition period -

The EU "notes" Britain's proposal for a two-year transition period from Brexit day, March 29 2019, but says the actual duration will have to be negotiated.

Talks on the transitional arrangements are set to start in January.

- No role in EU bodies -

During the transition period, the EU says Britain will not be able to "participate in or nominate or elect members of the EU institutions" or take part in any EU decision-making.

- EU rules to apply during transition -

The bloc says that all EU "regulatory, budgetary, supervisory, judiciary and enforcement instruments and structure" will apply to Britain during transition.

This would mean Britain would have to pay in to the EU budget and submit to its rules -- including new ones -- without having any say in Brussels.

- Britain still subject to ECJ -

The EU guidelines say that during the transition period, Britain would still have to follow rulings from the European Court of Justice.

Leaving the court's jurisdiction was a key demand of many Brexit supporters, who argued it was a crucial part of "taking back control".

- Freedom of movement -

Britain will remain in the EU's single market and customs union during transition, and the EU says this means it must respect the "four freedoms" -- including freedom of movement for European citizens.

Ending freedom of movement was another major demand for many who wanted Britain out of the EU. They argued it was necessary to reduce immigration.

- Trade -

The EU says Britain will have to follow the bloc's trade policy during transition, including on tariffs on goods from non-EU states.

Britain has been keen to pursue trade deals with the rest of the world, but an EU source said that while London would be free to negotiate agreements, they could not sign anything until after Brexit.

- Give us more clarity -

Brussels has repeatedly complained that London has not been clear enough about what it wants from Brexit and the guidelines urge Britain "to provide further clarity on its position on the framework for the future relationship".