A senior adviser to the prime minister has been questioned by police in the investigation into cash for honours, allegedly involving Labour donors.
Ms Turner stood for Labour in the 1999 European Parliament election
Ruth Turner is the director of government relations at Number 10 and was interviewed in London last week.
About a dozen people are believed to have been questioned so far. Three arrests have been made, although all have denied suggestions of wrong-doing.
The inquiry is looking into claims that wealthy backers received peerages.
And its scope has since been widened to cover similar allegations involving the Conservatives.
Head teacher Des Smith, who was on the council of the Specialist Schools and Academies Trust, was the first person to be arrested and bailed, in April.
He resigned from the Trust after allegedly telling an undercover Sunday Times reporter it was typical for people who made donations to his project to receive an honour.
Officers have also twice interviewed Labour's chief fundraiser - and Tony Blair's personal representative in the Middle East - Lord Levy.
And last week, the millionaire head of Biotech, Sir Christopher Evans, said he was "shocked and dismayed" to have been detained.
Ms Turner stood as a Labour candidate for the European Parliament in north-west England in 1999.
Her current department helps Downing Street to deal with Labour and the public.
It also arranges visits for Mr Blair as well as charity receptions and other events at Number 10.
Labour's treasurer, Jack Dromey, has refused to give his views on the latest development in the inquiry.
"Forgive me if I make no comment on the police investigation," he told BBC News 24.
"I've not said anything; I will not say anything in the future."