Politicians have completely failed to challenge the "Big Brotherish" behaviour of spying agencies exposed by US whistleblower Edward Snowden, the Green party leader has said.

Natalie Bennett, speaking at the party's conference, said the Liberal Democrats in particular should be "indicted" for staying silent as freedom comes under threat from mass surveillance.

The major parties have "utterly rolled over and accepted what the security establishment is saying" despite worrying evidence that spies are expanding their power without the public knowing, Bennett said.

Her remarks formed part of a series of cutting attacks on the major parties, who, she said, were "virtually indistinguishable". Bennett's keynote conference speech sought to broaden the appeal of the party by tackling more than simply environmental concerns.

The Green leader said her party would not rest until it ends the use of food banks, brings in a compulsory living wage, re-nationalises the railways and halts NHS privatisation.

"Labour is not a credible alternative to the coalition," she said. She attacked the party for refusing to say it would abolish the bedroom tax, failing to speak up for the rights of immigrants and saying benefit cuts "aren't deep enough".

Meanwhile, the Lib Dems have "failed to protect Britain" from fracking, secret courts, legal aid cuts, the lobbying bill and the surveillance state.

"We have seen the Lib Dems silent on the fate of courageous whistleblower Edward Snowden and we have seen Nick Clegg's spokesman explicitly endorsing the ridiculous but disturbing sight of security officers standing over Guardian journalists as they destroyed evidence at the government's behest," she said.

The Conservatives have been "spinning off a stream of profits to their friends" and handed over the NHS to "corporate bloodsuckers", she added. Condemning all further privatisation, Bennett said the party has now gone "where even Margaret Thatcher would not go" by selling off the Royal Mail.

As for Ukip, Nigel Farage needs to do more than "waving a pint and a cigarette" to be taken seriously, Bennett said, although the Green conference is offering a session on how to tap into "mass popular awareness" like the eurosceptic party.

The party leader, who took on the job a year ago, received a warm reception to the speech despite stumbling when her autocue failed at one point.

Meanwhile, Caroline Lucas, the Green party's only MP and former leader, described the coalition's cuts to welfare as "worse than the Victorian era".

The party's attempts to broaden its appeal comes as it trails far behind the major parties in the polls on just a few per cent of the vote. It has also been rocked by a dispute over bin collections in Brighton, which has set the Green-led council against Lucas, who supported striking workers.

Bennett acknowledged the party will face a tough fight to retain the Brighton parliamentary seat and control of the council.

However the former Guardian journalist, said a recent survey suggests the party is polling better than the Lib Dems when it comes to next year's European elections.