Well, interestingly Article 50 is mostly about procedure :
This summary of what Article 50 is and how it works from a European Parliament briefing paper:
The right of a Member State to withdraw from the European Union was introduced for*the first time with the Lisbon Treaty; the possibility of withdrawal was highly*controversial before that. Article 50 TEU does not set down any substantive conditions*for a Member State to be able to exercise its right to withdraw, rather it includes only*procedural requirements. It provides for the negotiation of a withdrawal agreement*between the EU and the withdrawing state, defining in particular the latter's future*relationship with the Union.
If no agreement is concluded within two years, that*state's membership ends automatically, unless the European Council and the Member*State concerned decide jointly to extend this period.
The legal consequence of a withdrawal from the EU is the end of the application of the*EU Treaties (and the Protocols thereto) in the state concerned from that point on. EU law ceases to apply in the withdrawing state, although any national acts adopted in*implementation or transposition of EU law would remain valid until the national*authorities decide to amend or repeal them. A withdrawal agreement would need to*address the phasing-out of EU financial programmes and other EU norms.
*The negotiators on the EU side may choose to play hard ball, to discourage others from following the UK’s example. Fabian Zuleeg, an analyst at the European Policy Centre told the Observer that it is not in their political interest “to concede a lot to the UK,"*
Source: independent newspaper
The upshot of this is, while it may suit Nigel Farage to negotiate slowly until 2020
Brussels may well call a halt to negotiations after two years, as a warning shot across the bows of France and Netherlands who already are chomping at the bit. Perhaps Nige didn't read that bit... In fact because of UKiP's continual disruption of the European Parliment over the years, he is the last person i would want negotiating the "best" deal possible. People like Junkers must be allergic to the very sound of his voice by this stage.