The Green party has launched its EU referendum campaign, promising to be “loud and proud” about backing Britain’s membership.

Caroline Lucas, the party’s only MP and board member of the Britain Stronger in Europe group, said mobilising hundreds of thousands of Green supporters would be crucial to the remain campaign.

Before the launch in Westminster, Lucas said: “We won’t sit idly by when our environmental protections and our rights at work are threatened by Brexit. Our campaign for British membership of the EU will be loud and it will be proud.

“In a fast-changing world we need international rules to control big business and finance, and to ensure that people’s rights are protected – at work and as consumers. The EU has also given us the freedom to live, study, work and retire across an entire continent.

“The EU helps us look after our environment, too. It’s only by working with our European neighbours that we can tackle climate change, protect wildlife and reduce pollution. Thanks to EU rules, our beaches are cleaner and our dirtiest power stations are being shut down.”

Lucas recently warned the UK was in danger of “sleepwalking” out of the EU without more vocal and active support from the Labour leadership. There have been wider fears among remain campaigners that the left is not mobilising enough support among its supporters and voters to get Britain to stay in the EU.

Pat McFadden, the Labour MP who lost his job as shadow Europe minister in the last reshuffle, made a plea for more active campaigning in favour of the in campaign this weekend at the Progress political event. “Labour is largely united on this question. The vast majority of our MPs and members want to stay in,” he said. “Yet we know we have not been heard enough so far in the Europe debate.

“Alan Johnson is arguing the case with passion, conviction and skill but we are not yet as much a part of this story as we can be. It is up to all of us to get behind Alan and do what we can for this campaign. As he rightly tells us, don’t wait for permission from him. The starting gun has been fired.

“Labour’s struggle should always be for victory, not relevance. We should not allow ourselves to be bit players while the future of the country is fought out between Conservative politicians more interested in their own next job than in the jobs, futures and living standards of millions of people in our country.

“This is a question of leadership and we have both a duty and an opportunity to show leadership on this issue, when the governing party is so divided.”

This article was written by Rowena Mason Political correspondent, for on Monday 14th March 2016 12.04 Europe/London © Guardian News and Media Limited 2010