The Guardian has a good explainer on how exactly a UK exit from the European Union (EU) could look:

Cameron has vowed if there is a Brexit vote he will trigger article 50, the part of the Lisbon treaty that sets in train a two-year process whereby a member state can notify the EU council of its decision to leave.

Constitutionally, the triggering of article 50 is a decision for him alone, not parliament, since it is a matter of the royal prerogative. At the same time, nothing can stop parliament passing a motion that seeks to instruct him not to trigger article 50.

However, the UK's exit needs to be ratified by EU member states representing 65 per cent of the EU population and if this does not happen, the UK will lose free trade privileges with Europe at that point while full exit continues being negotiated.

Of course, if we remember British constitutional law, the UK parliament has absolute sovereignty so it should in theory be able to expressly ignore or undo the electorate's referendum decision, but politically this would likely spell suicide for the main political parties.

And for UK international law firms, which mostly have massive operations throughout Europe, Brexit will be a massive blow...