On a drizzly morning last September, Zack Polanski delivered his first speech as leader of the Green Party. The avowed eco-populist, who won the leadership election with 84 per cent of the members’ vote, set out his party’s course: to deliver the growth in membership and poll ratings his predecessors could only have dreamed of. He made an audacious promise. “My message to Labour is very clear,” he said. “We’re not here to be disappointed by you. We’re not here to be concerned by you.