A candidate can be nominated by a Parliamentary Group - a party can form a Parliamentary Group if one of these conditions is met:
- It has at least one-thirtieth of the MPs, or
- It has at least one-sixtieth of the MPs, won more than 3% of the vote and contested more than two-thirds of constituencies (note that Greece has a combination of single-member and multi-member constituencies)
Any party that doesn't meet either of these criteria sits as part of the Independent Group, which also has the right to nominate a candidate. If this were applied to the House of Commons, then the first criterion would require 22 MPs, and the second 11 MPs - hence only the Conservatives, Labour and the Liberal Democrats would count as party Parliamentary Groups, with all other MPs forming the Independent Group.
There are 3 rounds of voting, with the electorate restricted to MPs. In the first, a candidate needs two-thirds of the vote to be elected. If not, then a second round is held 5 days later - again, with the two-thirds requirement.
If no-one is elected, then 5 days later there is another presidential election - and this time a candidate needs to reach a lower target, namely three-fifths of the vote.
If no President is elected, then Parliament has failed in one of its key duties, so fresh parliamentary elections have to be held. After these, there is again a 3-round process for electing the President. In the first round, again a three-fifths majority is needed. If this isn't achieved, then there is a second round 5 days later, where an absolute majority is needed. If this isn't successful, then 5 days later there is a run-off election between the top 2 candidates.