A senior adviser to British prime minister Tony Blair has been arrested in the "cash-for-honours" inquiry.
Downing Street aide Ruth Turner was arrested on suspicion of perverting the course of justice today by police investigating cash-for-honours allegations.
In a statement, Scotland Yard said she was taken to a London police station where she was interviewed and was later bailed pending further investigation.
Mr Blair immediately issued a statement in support of Ms Turner.
"Ruth is a person of the highest integrity for whom I have great regard and I continue to have complete confidence in her," Mr Blair said in the statement.
Ms Turner (36), was appointed as a Downing Street special adviser in May 2005, having previously served on Labour's ruling National Executive Committee and stood for the party in the 1999 elections to the European Parliament.
She becomes the fourth person - and the first salaried Government official - to be arrested in the inquiry, after Mr Blair's personal fundraiser Lord Levy, major Labour donor Sir Christopher Evans and headteacher Des Smith.
Police interviewed about 90 people as part of the investigation.
Ms Turner was previously interviewed under caution in September last year, reportedly in relation to emails uncovered by detectives during a search of Downing Street computer and paper files.
It was reported that police questions then centred on emails which appeared to have been sent to and from Ms Turner's Downing Street workstation, discussing which lenders might be placed on a list of nominees for peerages.
Mr Blair himself was questioned by police in December.
They began an inquiry in March into allegations that Labour and other political parties had nominated people for seats in parliament's upper house, the House of Lords, in exchange for party funding.
Police have interviewed most members of Mr Blair's 2005 cabinet. They wanted to know if ministers were aware that four rich businessmen who helped bankroll Labour's 2005 election campaign had been nominated by Mr Blair for peerages - titles that carry seats in the unelected House of Lords.
Mr Blair swept to victory in a landslide election win in 1997, promising Labour would be "whiter than white" and clean up politics after the previous Conservative government became mired in a series of financial and sex scandals.
But his popularity has plummeted over Iraq and a series of government scandals and reports of mismanagement. He is expected to hand over power later this year to Gordon Brown.
PA