Green Party leader Caroline Lucas has urged disgruntled Liberal Democrats to jump ship and "join us".
She told supporters of the junior coalition party who were "beginning to despair of the path their leadership has taken them down" that their contribution to politics is "more valuable than ever".
Addressing her party's autumn conference, which is being held in Sheffield, Ms Lucas said she had a "special message" for Lib Dems.
"If you became involved in politics to serve your local community, to protect the environment, or to challenge inequality, then join us," she said.
"We are working for the same ends. You'll find many former Lib Dems among our ranks. And your contribution to politics in our country is more valuable than ever."
Ms Lucas also criticised the "growing influence of big business" in Government, claiming Whitehall departments are using secondees from big business to advise ministers and help manage public services after axing highly paid consultants.
She added: "There are now so many that the Government has to admit that it can't count them all.
"It can't say even which companies they come from or what they're doing.
"Now there are very few businesses who will lend their top employees to Government for nothing.
"No, they expect something in return - influence, access, the inside track on the next fat contract. How typically Tory. What looks like a reform turns out to be making the situation even worse."
