No wonder the Labour alarm bells are ringing: new figures out today show the Greens have doubled their membership numbers in the last 11 months. This morning the Greens passed 27,618 members, which means membership is as its highest level ahead of a General Election since 1989. They picked up 500 members over the weekend alone. Just last week Guido noted the potential for a Green surge, while there are concerns in Labour circles that Sadiq Khan’s “the Greens are right, but vote for us” tactic isn’t working. The Greens are now rivalling UKIP as the fastest growing political party…