The payment would replace existing unemployment benefits, but would be paid to people with jobs as well as the unemployed.

The party says the policy would benefit the unemployed because they would not lose benefit income when they found work. It would also reinforce the incomes of people in work.

Bennett told BuzzFeed she regularly faced "extensive" questioning on the policy from audiences: "When I was first elected I hardly ever talked about citizen's income. That's changed in the last year; at the moment, I'm at the level that I probably talk about it extensively to an audience at least once or twice a week."

The universal income, sometimes called a "citizen's income", is a longstanding Green policy, but has not before featured prominently in the party's campaigns. Bennett added that her party was "ahead of the curve" on the issue, which has been the subject of a number of grassroots campaigns over the last year.

"The Citizen's Income Trust has got a lot bigger and stronger, we had an EU citizens' initiative campaign to try and bring it in, and Switzerland is having the referendum on it. As an idea it's very much risen, and we're ahead of the curve."

Other policies set to feature prominently in the Green election campaign are a wealth tax of the kind advocated by "rock star" economist Thomas Piketty, and an increase in the minimum wage to a living wage. Bennett said there would be more announcements to come.