Former deputy prime minister Nick Clegg has called for centrist Labour and Conservative politicians to unite and mount "a proper ideological response" to Theresa May's government.
The Liberal Democrats' Europe spokesman branded Brexit "an ideological coup" that could pave the way for cuts to welfare and workers' rights.
Mr Clegg also used an interview with The Guardian to attack "a curious cabal of old men" who ran the British establishment, dismissing suggestions it was "conspiracy stuff".
"No one can beat the Conservatives on their own so it's not that complicated – we're condemned to work together," he told the newspaper.
"I would welcome and embrace more thinking and writing and talking and speaking amongst liberal Conservatives, one-nation Conservatives, Liberal Democrats, centre-ground Labour folk who want to mount a proper ideological response to that."
Former Lib Dem leader Mr Clegg welcomed Tony Blair's new Institute for Global Change, which aims to re-energise the centre ground, and suggested there could be more scope for Labour and the Lib Dems to work together in a bid to fight the Government's push for a hard Brexit.
He said this cross-party work would not involve a new organisation, though, but rather "defining our enemy" and seeking to represent the needs of younger people.
Mr Clegg added: "What lurks behind Brexit is an ideological coup, in many ways a domestic one.
"Brexit is a means by which a low-state, low-protection, low-welfare, libertarian approach to governance is seeking to take over the commanding heights of British politics."
He said this was not "conspiracy stuff", adding that Britain was being run by a "curious cabal of old men", namely the power brokers on Britain's pro-Brexit newspapers – the Telegraph's Barclay brothers, the Sun's Rupert Murdoch and the Daily Mail's Paul Dacre.
Describing them as puppet masters, he said they wanted to turn Britain into an offshore economy, calling them a "bunch of old men – not elected by anybody – (with) Theresa May as their hostage".