Our cover this week is on the most important election in Britain for many years. Voters face a stark choice between Boris Johnson, whose Tories promise a hard Brexit, and Jeremy Corbyn, whose Labour Party plans to “rewrite the rules of the economy” along radical socialist lines. Mr Johnson runs the most unpopular new government on record; Mr Corbyn is the most unpopular leader of the opposition. That leaves a low bar for the Liberal Democrats and, for all their faults, they clear it. Their economic approach is the most sensible; on climate change and social policy they strike the best balance between ambition and realism. Yet they will not win. So why back them? The principled reason is that the Lib Dems are closest to the liberalism on which this newspaper was founded. But there is a practical reason, too. Voters worry that backing the Lib Dems plays into Mr Corbyn’s hands. However, our modelling suggests that votes and seats would come from both the main parties. A Lib Dem surge would be the best way to restrain whoever ends up in Downing Street.