A?qualified majority?shall be defined in accordance with Article 238(3)(b) of the Treaty on the Functioning of the European Union.
Nic Robertson CNN’s international diplomatic editor Nic Robertson writes:
Some analysis

Once article 50 is triggered, Britain’s Theresa May and her ministers will no longer be party to the remaining 27 EU member nations discussions. However, Britain is not officially out of the EU until the terms of Brexit are negotiated and agreed. In the European Parliament Britain’s voice will continue to be heard, however its relevance and impact will be on a decline.

Max Foster CNN’s Max Foster writes:
A bit of background

Article 50 says there can be no involvement of the withdrawing member state at Commission or Council level during the negotiations, but there is no rule for the Parliament. So British MEPs will still be able to vote on whether?or not?they are happy with the deal before?it is?passed back to the Council for sign-off.

A?qualified majority?is needed for a deal to be adopted. There are two criteria that define a qualified majority; the first of which means at least 55% or 20 of the remaining 27 member states will have to vote for the deal on offer. The second is that the approved vote needs to represent 65% of the European population. This means a deal can’t be approved without the big countries like Germany, France and Italy. But these three alone aren’t enough to hit the magic 65%, and so smaller countries like Belgium and the Czech Republic will also need to consent.?

5. If a?State which has withdrawn from the Union asks to rejoin, its request shall be subject to the procedure referred to in?Article 49.
Nic Robertson CNN’s international diplomatic editor Nic Robertson writes:
Some context

Like any nation that wants to become a member, Britain will have the right to ask to rejoin. It will however be expected to follow the same lengthy and rigorous procedures that any other applicant would follow.

Some in Europe sincerely hope Britain backs out of Brexit before the two years of negotiations are done. By then, however, negotiations may have become so fraught that desire for Britain to backpedal will be lost. Equally, the EU may find Britain’s Brexit so distasteful that a cooling off period may be needed before they'd countenance the UK’s return.

A bit of background

Article 49 is the framework for applying for membership to the European Union. It?reads:

Any European State which respects the values referred to in Article 2 and is committed to promoting them may apply to become a member of the Union. The European Parliament and national Parliaments shall be notified of this application. The applicant State shall address its application to the Council, which shall act unanimously after consulting the Commission and after receiving the assent of the European Parliament, which shall act by an absolute majority of its component members. The conditions of admission and the adjustments to the Treaties on which the Union is founded, which such admission entails, shall be the subject of an agreement between the Member States and the applicant State. This agreement shall be submitted for ratification by all the contracting States in accordance with their respective constitutional requirements. The conditions of eligibility agreed upon by the European Council shall be taken into account.