British authorities have arrested a seventh person as part of a historic crackdown on an insider trading ring that has sent shockwaves through the country's financial industry.

The Financial Services Authority (FSA) and the Serious Organised Crime Agency (SOCA), a special police unit, said on Wednesday the seventh individual, who remains unnamed, would be released on bail after questioning. They declined to comment further.

The latest arrest comes a day after the FSA and SOCA detained six men including Martyn Dodgson, a managing director at Deutsche Bank, and Clive Roberts, the head of European sales at BNP Paribas's partly-owned Exane unit, on suspicion of involvement in a long-running and sophisticated insider dealing ring.

Industry sources named Julian Rifat, an equity trader from U.S. hedge fund Moore Capital and Graeme Shelley, a trader at brokerage Novum Securities as among the people questioned.

UK media named two other people questioned as part of the investigation, but Reuters was unable to reach them.

Exane said Roberts had been suspended and Deutsche said Dodgson had been suspended pending the investigation. Moore Capital said Rifat had "been placed on administrative leave pending completion of the investigation." Novum said Shelley was "taking some time off."

SPEEDY CHARGES?

Tuesday's swoop was seen as an attempt by regulators to show their crime-fighting credentials, with a high profile case seen as the best deterrent to insider dealing.

Some lawyers said that while the FSA had in the past taken months to charge suspects after raids, this case -- which in volved more than two years of surveillance and a squad of almost 145 officers -- appeared to be at a more advanced stage.

"This bears the hallmarks of being a fairly advanced investigation," said Nathan Willmott, a partner at law firm Berwin Leighton Paisner. "There are indications that in this case the FSA may well be in a position to lay charges against individuals in a period of days rather than weeks or months."

The FSA and SOCA declined to comment.

The arrests, after the FSA and SOCA launched simultaneous dawn raids on 16 residential and business premises across southern England, sent shockwaves through the London's financial centre and bankers warned reputations could be shredded.

"There is a great risk that reputations could be severely damaged -- although many other banks are involved," said one financier at an involved financial institution. "The heads of our investment banking division are furious."

A lawyer who declined to be named said although the investigation was comprehensive with many people involved, the FSA might take time to assimilate all the information it has gathered.

The FSA and SOCA declined to name the suspects or divulge whether any had been bailed and when individuals might be charged.

"How long is a piece of string?" asked a SOCA spokesman, referring how long it would take for charges to be laid. The FSA said only: "As soon as we are able to comment we will...The investigation has been long-running and there is a lot more work to be done."

The FSA has toughened up its enforcement policy after years of being criticised for not doing enough to stop market abuse. In 2009, it levied a record level of fines and launched its first two successful criminal prosecutions.

Separately, Britain's Serious Fraud Office arrested three directors of French engineering group Alstom on suspicion of bribery and corruption after raids on nine properties in the UK on Wednesday.

The SFO said in a statement it suspected bribes were paid in order to win contracts overseas and that this had involved associated money laundering and other offences.

(Additional reporting by Louise Heavens and Laurence Fletcher in London, and Philipp Halstrick in Frankfurt; editing by Karen Foster and Elaine Hardcastle)