MAJORITY BUILDER: Select the hexagons to add-and-remove seats to-and-from the two major party totals. Compare actual results with a selection of other forecasts.

TO FORM a government in Britain, it is not enough for a party to win the most seats in the House of Commons. It must also command a majority there. If it cannot do that alone, it must rely on other parties. The interactive "majority builder" above allows readers to experiment with optional seat distributions using the 2015election results and a selection of latest polls.

INTERACTIVE: Compare Britain's Certain small parties are much more likely to support one of the Conservatives and Labour, Britain's two main parties, than the other. They are listed next to the party to which they are closest. The Liberal Democrats, in the middle, have declared themselves willing to work with either. To form a government, one of the main parties needs a majority of the 650 MPs; in practice, 323 of them.

Find more election graphics on our "data hub" here.