Police called in as defector accused of downloading party information

South Yorkshire Chief Constable Meredydd Hughes will be asked by the Liberal Democrats to investigate allegations that Sheffield city councillor Ben Curran downloaded information from a party database of voters shortly before swapping allegiance. A letter to Mr Hughes is calling for an investigation into whether there has been a breach of the Data Protection Act.

The deputy leader of the Liberal Democrat group in Sheffield, David Baker, said last night: "Clearly this is a very serious issue, that's why we are asking the Labour Party to give

an explanation and fully co-operate with a police investigation."

Labour announced the defection of Coun Curran on Friday, the eve of the Liberal Democrat party conference in Liverpool.

He said he was "disillusioned" at the way Nick Clegg's party had signed up to a programme of spending cuts.

He was welcomed to Labour by leadership contender David Miliband.

But the Liberal Democrats claim that before his defection, Coun Curran accessed a database containing personal information on thousands of voters in the city – including their voting intentions – which was built up through party campaigning and canvassing.

The information, which all parties collect, was allegedly downloaded onto a memory stick which the Liberal Democrats say has not been returned.

In his letter to Mr Hughes, Coun Baker said the data is believed to include information on people's voting intentions which had been volunteered to the Liberal Democrats on the basis they would not share it with any other organisation.

He claimed: "In addition other personal information such as mobile phone numbers, e-mail addresses and even in some cases details of casework carried out by Liberal Democrat local councillors was obtained."

The party has asked for an investigation, and has also called for the memory stick to be returned with a pledge that the information will not be used.

Coun Baker said he was "extremely concerned and angered" and he believed local people had the right to know how their personal information would be used.

Coun Curran singled out the "disgraceful" decision to cancel the 80m loan to steelmaker Forgemasters as a particular low point in his decision to defect.

"My personal values haven't changed but the political landscape has," he said.

A spokesman for Yorkshire and the Humber Labour Party said last night: "We have not received any data."

Coun Curran was unavailable for comment.