Why are voters in Northern Ireland poised for a return to the polls?

Northern Ireland Secretary Chris Heaton-Harris has made it clear he will call a fresh poll if the deadline passes, with December 15 the likely date (Liam McBurney/PA)

Voters in Northern Ireland face the prospect of returning to the polls in December, a little over seven months after the last Assembly election.

Here are answers to some of the key questions about the political turmoil at Stormont.