Nick Clegg knew of Lord Rennard 'concerns' in 2008
Liberal Democrat leader Nick Clegg says he was made aware in 2008 of "indirect and non-specific concerns" about the party's then-chief executive.
Lord Rennard had been "warned" at the time but "categorically denied that he had behaved inappropriately and he continues to do so", Mr Clegg said.
The deputy PM said he had not known until last week about claims of alleged sexually inappropriate behaviour by the peer made by a number of women.
The party is to review the complaints.
The inquiry under the party's disciplinary procedures will also look at whether Lord Rennard stood down in 2009, after six years as chief executive, for reasons other than the health grounds stated at the time.
On Thursday and Friday, Channel 4 News broadcast allegations by four women of sexual impropriety by Lord Rennard in incidents spanning several years, the first in 2003.
'Angry and outraged'
Some reports questioned if Mr Clegg, who was on holiday on Spain when the story surfaced, had known of the claims years ago.
In a statement on Sunday, Mr Clegg, who became party leader in 2007, said: "I am angry and outraged at the suggestion that I would not have acted if these allegations had been put to me.
"Indeed, when indirect and non-specific concerns about Chris Rennard's conduct reached my office in 2008, we acted to deal with them."
Mr Clegg said the "concerns" had been put to Lord Rennard by his then-chief of staff Danny Alexander, who "warned him that any such behaviour was wholly unacceptable".
"Chris Rennard categorically denied that he had behaved inappropriately and he continues to do so. He subsequently resigned as chief executive on health grounds."
In his statement, Mr Clegg added: "As my office only received concerns indirectly and anonymously, as those involved understandably wanted to maintain their privacy, there was a limit to how we could take this matter forward following Chris Rennard's resignation.
He said the Channel 4 broadcast showed that there were "legitimate concerns that issues raised with the party were not handled as well as they should have been" and the party review would examine this.
Ahead of Mr Clegg's statement, BBC political correspondent Iain Watson said: "I think privately he feels that this controversy isn't so much about Lord Rennard, there's an attempt to undermine him and his party leadership.
"Lib Dems themselves would admit that, in the run-up to a crucial by-election, these allegations haven't come at a good time."
Later on Sunday, Mr Alexander said in a statement: "The party has rightly set up inquiries into these matters and I will participate fully in those processes."
Two women told Channel 4 Lord Rennard had abused his position by inappropriately touching and propositioning them.
One of the women said she had spoken to two senior party figures about her claims, but said no action had been taken. Allegations from more women were broadcast on Friday.
"Gradually his hand started to rub the outside of my leg," one of the women - a very active member of the Lib Dems - told Channel 4.
"I thought at first he'd just brushed against me. Then I moved away and it happened again. And he moved closer - and I moved away again. And he moved closer, and he just kept brushing parts of me that I didn't want to be brushed."
Mr Clegg's former parliamentary aide, Jo Swinson, and now equalities minister, has said she "took action" after some women had confided in her, but she has not specified what form that action took.
The Mail on Sunday reported that one of the women who came forward to Channel 4 News had discussed the allegations with a friend on Facebook in January 2009.
"I just don't know how nick can know and not do anything.. :-( makes me very sad," she wrote, according to the paper.
Lord Rennard, who was also a key strategist and adviser to a succession of party leaders, said on Friday he was "deeply shocked" about the allegations and said they were a "total distortion" of his character.
The peer said he knew of no complaints against him in his 27 years working for the party, but he has temporarily stood aside from the Lib Dems' group in the Lords to avoid "embarrassment" to the party.