Last week, after over 30 years of being a Labour party member, I left – and joined the Green party. The events of that week were the final straw for me. It had already become clear that the Labour party was never going to recover from the poison of Blairism and return to being the radical campaigning force for social change it once was.

Having come a poor third in the Rochester byelection, a seat that had been held by Labour until 2010, and after Ed Miliband’s disastrous handling of the Emily Thornberry white van fiasco, it became obvious to me that there wasn’t even a realistic prospect of a centrist Labour defeating the Tories in 2015.

I joined the Labour party in the early 1980s to take a stand against the Thatcherite attacks on the welfare state, put in place after the war. Although there were fierce arguments about the way forward, there was no doubt about the party’s identity, firmly based as it was in the Labour movement, as the party of working people. It was also a democratic organisation where members were able to change party policy at party conference.

Blair and New Labour’s distancing from the Labour movement and embrace of “the market” as the answer to Britain’s problems, rather than the reversing of Tory attacks on the marginalised sections of our society, delivered a critical blow to Labour. The slavish following of George W Bush, with his reactionary and misguided foreign policy of regime change, into the Iraq war was appalling. It ended any hope of an ethical foreign policy.

New Labour wrongly obsessed about choice – in pensions, health and education. Unfortunately it deprived us of the most important choice – the choice of the Labour party as a radical alternative to the Tories.

I voted for Ed Miliband in the 2010 leadership election. He seemed to me to hold the best prospect of a clear shift away from the awful legacy of New Labour. Unfortunately, that has not happened. Perhaps it was unrealistic to think it could happen, since the whole current generation of Labour politicians collaborated without protest in Blair’s government.

When they oppose the policies of the government they are met with the response that the coalition is only continuing the work started by New Labour. The most graphic example of this is Andy Burnham’s vocal opposition to privatisation of the NHS. The Tories are right to point out that this was the Labour government’s policy when he was health secretary.

Labour’s jumping on the Ukip anti-immigration bandwagon reflects the party leadership’s lack of clear direction. Unwilling to take a principled stand on such fundamental issues, they prefer to take a populist position in the hope of winning a few more votes. The Rochester byelection result, and the opinion polls, show that they are lurching towards a defeat next year, which will let the Tories back in to carry on their reactionary agenda that looks after their rich and powerful friends.

Until recently, there has been no credible radical campaigning force in British politics. Over the last decade or so I have met so many people who share my views but who couldn’t find a political home. Many of them have now joined the Greens. The election of Caroline Lucas in Brighton in 2010 and new Green councillors around the country building on the European parliament and London assembly seats is creating a critical mass for real progressive change in Britain.

The Green surge this year, both in membership and support in the opinion polls (at the same time as the Lib Dem collapse), means that in many areas it provides a real alternative political voice. It is an organisation with a democratic structure where members decide party policy, and its radical programme reflects many of my socialist views. Refreshingly, women play leading roles.

The current two-and-a-half-party setup is facing major challenges but not just, as the media suggests, from Ukip on the radical right. The next year provides an opportunity for the Greens to become the strong left voice Britain so desperately needs. I’m going to play my part in making sure this happens.