London Green Party and its Mayoral candidate Jenny Jones will recommend that supporters cast their second-preference vote for Ken Livingstone in the May election.

Members made the decision after being addressed by Livingstone at a meeting on Monday, but the result was kept under wraps until tonight.

Ken Livingstone has already repeatedly called for his voters to cast their second vote for Jenny Jones, making it clear this recommendation was not dependent on a reciprocal one from the Greens. But members chose to return the favour, and the campaign has adopted the slogan Jen 1, Ken 2 to communicate the endorsement.

London Green Party members made a similar decision in 2008, when then-candidate Siân Berry announced the deal in a press conference alongside Livingstone.

However, this is the first time Livingstone has appeared in person at a Green Party meeting to appeal to members for their second preferences.

The London Mayor is elected under the Supplementary Vote system, a limited form of AV. If one candidate receives 50% of the first preference vote they are elected, otherwise all but the top two candidates are eliminated and second-preference votes are added to their totals. Voters mark only a first and a second vote, not as many numbers as they wish under full AV or STV systems.