If it is really close both will be working hard to form partnerships so they can show the Crown they have the right to form a Government. The party with the biggest block of seats(including List) but a theoretical minority is usually invited first, they will be asked if they believe they can govern either with coalition partners or alone as a minority Government. That is a nightmare position and one we may well find ourselves in. It is why I have been saying I believe there will be an election well before 2020.