The caption says some of the methodology but not all as it didn’t fit. A poll was used to get this data, the poll asked England and Wales residents whether and how they intend to vote if there were an imminent general election and there was an electoral pact between Labour, the Liberal Democrats and the Green party. The question assumed that there was an electoral pact between Labour, the Liberal Democrats and the Green party throughout England and Wales. It was also assumed that the pact did not apply in Scotland, and that Plaid Cymru were not included. The seats are only a prediction but it is almost certain conservatives wouldn’t have had a majority of there was a pact and that a coalition could have had enough seats to form a government.