Talks have been held involving, among others, Christian Aid, Friends of the Earth and Charter 88.
The moves come as opinion polls, and membership figures of green groups, show the environment slipping down the national agenda. At the same time, some disillusioned Green Party deserters are considering forming a new a political party.
Last autumn, several leading Green Party figures, led by Ms Parkin, decided not to run again for elected office or resigned posts. Some, but not her, dropped their party membership. Several have formed Green Realignment, which holds an inaugural conference this weekend: 300 people have been invited to a converted chapel in Twickenham, west London. Ms Parkin is among the speakers.
The Green Realignment rebels had been on the party's pragmatic wing, concerned with streamlining decision-making and sharpening the party's image. They suffered a series of defeats last year.
'The old guard of ageing hippies and eco-anarchists threw out the whole professional approach,' said Lou Betts, a former party executive member and organiser of Green Realignment.
Mr Betts said forming a new party was an option, but no quick decision would be made. 'Perhaps in five years there can be a reconciliation.' None the less, one of the new group's declared aims is 'to create a coherent strategy to further green politics with the intention of taking an active part in the electoral process'.
Mr Porritt, who retains his party membership despite having voiced strong doubts about its leadership, said: 'I've made my views clear to Green Realignment - the idea of a new party is pretty crazy.'
Jean Lambert, one of the two Green Party speakers, said the party had sharpened its organisation and campaigning since the rebels' departure. In last month's county council elections, it won 5 per cent of the votes where it fielded candidates.
Meanwhile, Mr Porritt and Ms Parkin have been meeting directors of green organisations, Third World development charities and Charter 88 in the hope of forming a loose alliance of progressive, socially concerned groups.
Eventually they hope to involve some of the 'poverty lobby' - groups such as the homelessness charity Shelter. The aim is to gain more clout through what they perceive as one broad, diverse movement supported by millions.
A key theme in the talks is sustainable development - that today's generation should not enrich itself in ways which damage the prospects of future generations. Mr Porritt said the Liberal Democrats and Labour were not ready to be a vehicle for the 'sustainability' movement.