Police could be called in to investigate "incredibly serious" allegations of voter intimidation in an inner London borough, Deputy Prime Minister Nick Clegg has indicated.

The Electoral Commission has announced it will look into the problems in Tower Hamlets, where it took five days to count the votes in a local election which saw Labour finish narrowly ahead of the party of re-elected mayor Lutfur Rahman.

Mr Clegg said if the allegations of intimidation turn out to be of a "criminal nature", then the police will need to investigate.

He accused Mr Rahman's Tower Hamlets First movement of "arrogance".

Mr Clegg told LBC radio that the Electoral Commission " are going to look into these allegations of very serious, if those allegations turn out to be true, incredibly serious allegations of intimidation".

He said: "If those 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."

Accusing Mr Rahman's party of being arrogant, he said " somehow they appear to think they can swagger about in Tower Hamlets and do what they like" but "this is a mature democracy".

"Let the Electoral Commission do what they said, let them look into this. We have got to bring the police in if those allegations turn out to be of a criminal nature."

Mr Rahman, who split from Labour in 2010, was re-elected as mayor but Labour won 20 seats on the council to Tower Hamlets First's 18. The Conservatives won four seats, meaning the authority has fallen to no overall control.