Robin Harper: I am a builder not a destroyer - that's why I had to leave the Scottish Greens

Friday 4th August: My 83rd birthday. The fuss has all died down. I’ve had a great deal of positive reaction – certainly enough to reinforce my decision – and there will be some people who may never forgive me. That’s life.

People are still asking me ‘why’? It’s simple. After I left parliament I remained active in the environment NGO sector, but recently an opportunity to become politically active again presented itself. Gordon Brown and his team of researchers have set up a group called Our Scottish Future. The aim of this group is to get people throughout the UK talking about how to improve the functioning of our UK democracy.

For the last thirty years or so, we have been debating independence in Scotland. The same arguments for and against have been endlessly repeated and almost every poll on the subject shows we are close to evenly divided. You cannot build a new country on a foundation that is cracked down the centre – whatever happens the final decision would leave half the nation delighted but the other half deeply and permanently dismayed. There has been no consideration of an alternative. It is about time we looked at ways to mend and improve what we have rather than take a wrecking ball to a constitution that has largely served us well for three centuries and that still supports one of the richest and most peaceful nations in the world.

If Our Scottish Future is successful, we hope to have persuaded at least one political party (probably Labour) to adopt a commitment to a top to bottom revision and rebuilding of our democratic system. I find this exciting and invigorating, and I want to be part of it. Being a member of a party that seeks to destroy the UK is not compatible with the aims of Our Scottish Future. I had to leave the Scottish Green Party.

I am a builder not a destroyer. I dedicated most of my active life between 1985 and 2011 to the Scottish Greens. From 300 members of the Scottish Ecology Party in 1985 with not a single elected representative, there is now a huge membership with 35 councillors and seven MSPs in the chamber, plus the Presiding Officer. All this with a huge effort from a relatively small team, of which I am proud to have been a member.

However, I am seriously concerned by many aspects of the Green performance in the parliament and by the general tone of how they conduct their business. The party has moved to the left and seems to have forgotten that there is also a centre in Scottish politics, which should not be ignored. Eighteen months ago, at the end of a meeting of a local environmental group, I mentioned casually to my Green councillor that I had concerns about our gender legislation and was going to voice them. The next thing I knew was that he had reported the conversation to the party’s standards committee, who issued an admonitory letter and commanded my attendance at a meeting to talk things through. This is the sort of thing you expect in extreme left and right organisations. I didn’t expect it of the Green party. In my world, thorough and open debate and a clear-headed examination of evidence is vital as a precursor to sound legislation.

I am disturbed that our leading quadrumvirate – Harvie, Slater, Chapman and Greer – are all in too much of a hurry to get their ideas on the statute book and are not using what I would call due diligence. There is also a suspicion that if they did know that neither the gender nor the recycling legislation would be approved by Westminster, they went ahead in the full knowledge that the situation could be exploited to produce yet another instance of the SNP policy of manufactured grievance against Westminster.

I am very sad to have left the party, but equally glad to have a new focus for my energies. A rejuvenated efficient, co-operative, economically sound United Kingdom is an inspiring objective and we could all get round it.