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Nick Clegg today accused the controversial mayor of Tower Hamlets of "arrogance" as he backed an investigation into the borough's chaotic election process.

The Deputy Prime Minister launched an extraordinary attack on Lutfur Rahman amid allegations of voter intimidation at polling stations – and said police should be called in if the claims are found to be true.

Watchdog the Electoral Commission has confirmed an investigation into what happened after claims of "arguments, threats and chaos" at the vote count.

Speaking on his LBC Radio show, Call Clegg, the Lib Dem leader said: "I totally share your anger about what is alleged to have happened. I want the Electoral Commission to do what they said they were going to do and look into these incredibly serious allegations of intimidation.

"If these allegations do turn out to be of a criminal nature where people are being intimidated from allowing the democratic process to run its course then of course the police need to be called in."

A key adviser to Mr Rahman yesterday warned that violence will "spill onto the streets" if the results of the election were not accepted. The controversial mayor narrowly defeated a challenge by Labour's John Biggs to secure four more years of power at last week's polls.

But Mr Clegg today branded the warning "outrageous" during a scathing attack on Mr Rahman's newly-formed Tower Hamlets First party.

"I find the whole Tower Hamlets First movement and the pronouncements of Lutfur Rahman... just the kind of arrogance of it that they can swagger about in Tower Hamlets and do what they like."

He went on: "This is a democracy. This is a mature democracy, and you neber try and even suggest that you have a right to kind of push people about when democracy is all about people pushing politicians about, not the other way round."

Labour and Mr Rahman's party are now battling to secure a majority in the council chamber, with a crucial by-election still to be held after a candidate's sudden death.