The Greens today sought to gatecrash Charles Kennedy's party when they urged people angry about the invasion of Iraq to vote for them instead of the Liberal Democrats, who they alleged opposed military action only after market research told them to.

With their spring conference clashing with that of the Liberal Democrats, the Green party spokesman Keith Taylor accused Mr Kennedy's party of feeding at the corporate trough and backing the government's agenda of privatisation. Mr Taylor - who, along with the Green MEP Caroline Lucas, is the party's principal speaker - is the Greens' best hope of winning a parliamentary seat, having come a good fourth in Brighton Pavilion with nearly 10% of the vote in 2001.

However, even he conceded that victory in the seaside city was a long shot, and instead hoped his campaign - and those of the Greens' 200 other parliamentary candidates - would propel the party onto greater electoral successes in future local, devolved and European votes.

With seven seats in the Scottish parliament, two in the European parliament and sizeable numbers of councillors in university cities such as Oxford and Brighton, the Greens have been well served by proportional representation and determined local campaigning.

Leading members are, however, concerned that the party could be squeezed by the Liberal Democrats at the forthcoming general election, with many disillusioned Labour voters opting for Charles Kennedy's rather milder brand of radicalism.

Mr Taylor asked delegates gathered in Chesterfield: "How can the Lib Dems be a real voice of opposition when they accept the government's agenda of privatisation, when they recently opposed congestion charging in Edinburgh, and when they only turned against the war on Iraq after their market research told them to do so?

"We shall be fighting in around 200 seats, 30% of those available - that's not bad for a party that does not feed at the corporate trough, at which I see the latest snout swallowing big business bucks belongs to the Lib Dems. They've obviously given up all hopes of street cred."

Mr Taylor also attacked Labour's record on the environment, pointing out that despite Mr Blair flagging up the issue of climate change as the "number one challenge facing the world", he had failed to include it on the party's pledge card.

Delegates later voted to back an election platform committed to scrapping foundation hospitals, renationalising the railways and ending top up fees and the private finance initiative.