In his speech to the Liberal Democrat conference, deputy PM said Ukip and SNP offer ‘false comfort of grievance’ to voters

British politics is threatened by a divisive “us-versus-them” approach championed by Nigel Farage and Alex Salmond which offers a “false comfort of grievance” to voters, Nick Clegg has warned.

In his speech to the Liberal Democrat conference in Glasgow, the deputy prime minister said the Ukip and SNP leaders are making “seductive and beguiling” offers that are no more than a “counsel of despair”.

The strong attack on Farage and Salmond, the day before Ukip is likely to win its first Westminster seat in the Clacton byelection, was designed to highlight Clegg’s main pre-election pitch that he leads the only UK party rooted in the centre ground.

But the deputy prime minister also directly addressed one of his main personal weaknesses – that he is untrustworthy after his U-turn on university tuition fees – when he admitted that he had damaged trust in politics.

Promising that he would “never, ever” make the same mistake again, Clegg said: “In what might be the least fashionable statement made by any party leader this conference season – politicians of every party have fed this growing cynicism by exaggerating and overstating what governments can do. We’ve all done it. I’ve been there. When I apologised for the disappointment and anger caused by our inability to scrap tuition fees, I knew we could never, ever make that mistake again.”

In his speech Clegg also:

• Attacked the home secretary, Theresa May, for suggesting that Lib Dem opposition to the so called “snooper’s charter” is risking the safety of children. “Stop playing party politics with national security,” he told May as he warned that a “big brother state” demanding the storage of information on websites people visit is as threatening as a state that fails to protect children.

• Accused the Tories of assuming that every worry in the world can be solved by a “big wave of the Union Jack” as he condemned George Osborne’s plan to penalise the working age poor by planning to freeze benefits.

• Warned that Ed Miliband is promising an unrealistic “nirvana where everyone will be well-off, no one will be out of pocket”.

Clegg opened his speech with a strong condemnation of Islamic State whose beheading of Alan Henning and David Haines had given British military forces a “clear single objective”. He said: “To Isil we say this: all you have done is unite the people of Britain – Muslim and non-Muslim, people of all faiths and none – around a single aim. All you have done is give the British forces who are being deployed to Iraq – some of the best professionals in the world – a clear, single objective.”

Clegg hailed the result of the Scottish referendum as he quoted the comic pub landlord Al Murray who told the pro-UK rally in Trafalgar Square that there was something wonderfully vague about being British which he called “Brit-Ish”.

But the deputy prime minister had harsh words for Salmond and for Farage for seeking to promote a divisive form of politics. He said: “Something very un-British is taking root in our politics. A growing movement of people who want to pull us apart. Salmond, Farage, the bitter tribalism of left and right – in their different ways they’re all doing the same thing. A growing pick-a-side politics, in a world of us-versus-them. Worried about your job? Your business? Your children’s future? Your way of life? No matter, just blame Europe/Brussels/foreigners/immigrants/the English/the South/professional politicians/Westminster/big business/anybody claiming benefits/even onshore wind farms.

“Life is so simple when you know who – or what – to blame. It’s seductive and it’s beguiling. That much may even be proved tomorrow, if the people of Clacton give the UK Independence Party an MP. But resentment, the politics of fear, doesn’t pay the bills or create a single job. Claiming to address people’s acute anxiety about the modern world, it provides nothing but the false comfort of grievance. Dressed up as the politics of hope, it is in fact a counsel of despair.”