The woman at the centre of the Liberal Democrat sexual harassment scandal has defended Treasury Chief Secretary Danny Alexander as she warned other parties to brace themselves for similar allegations.

Former Aberdeen councillor Alison Smith said she had no doubts about the Highland MP's integrity after it emerged he had confronted the party's former chief executive Lord Rennard in 2008 over rumours of his alleged misconduct.

Ms Smith said she thought Mr Alexander's role during the talks in Nick Clegg's office was limited to talking to the peer. It came as the LibDems launched an investigation into its handling of the claims.

Ms Smith rejected suggestions the former federal party chief executive could make or break the careers of people like Mr Alexander. She said: "Rennard's reach didn't really extend to Scotland – the Scottish party has their own headquarters, their own executive committee, their own means of distributing funding, their own conferences and events.

"So the problems described in Westminister do not apply in Scotland, to my knowledge."

Ms Smith also warned other parties they could face similar accusations and should start "bracing themselves". The politics lecturer and four other women are thought to have contacted police over the claims, which the peer denies.

Meanwhile, Labour MP Gisela Stuart revealed how she had once had to threaten a Tory MP who was being a sex pest.

Ms Stuart said when he got too close she told him "you've got about five seconds to shift, after which my knee will be in a place which you will remember for a very, very long time".

Paddy Ashdown's former press secretary said women should "toughen up" in careers like politics. Jo Phillips said: "You're going into a tough world in politics. It's tough for men and women. There's a lot of bullying, nastiness, appalling behaviour you'd never get away with outside politics – you have to toughen up."

Former prime minister John Major's ex-press secretary Sheila Gunn said she had twice been the victim of sexual harassment from a senior Tory MP.

Mr Clegg has said he wants the investigations into the allegations against Lord Rennard done as quickly as possible.

David Cameron refused to back his handling of the issue. He said: "These are serious issues and they need to be taken seriously."

l Tory MP for Lincoln Karl McCartney has apologised for writing offensive notes to staff processing his expenses claims. The parliamentary standards authority said he had sent messages abusing officials.