Derek Hatton arrested in Liverpool building contracts bribery probe
Derek Hatton, the former deputy leader of Liverpool City Council, was one of five men arrested alongside the mayor of Liverpool, the BBC has learned.
Joe Anderson was held on Friday on suspicion of conspiracy to commit bribery and witness intimidation.
It is understood Mr Hatton was held on suspicion of witness intimidation, as part of a probe into the awarding of building contracts in the city.
All five men have been released on conditional bail.
Mr Hatton, 72, is a former deputy leader of Liverpool City Council and was a key figure in Militant, a far-left group that ran the city council in the early 1980s.
His membership of Militant led to him being expelled from the Labour Party in the late 1980s.
He then turned to property development, broadcasting and public speaking.
Mr Anderson has been suspended by Labour while the police inquiry continues.
In a statement, he said he was "co-operating fully" with the police.
Mr Hatton has not commented.
Merseyside Police has confirmed five men have been released on conditional bail, pending further inquiries.