On Friday the Conservatives suspended MP Charlie Elphicke after “serious allegations” were referred to the police, but the party has provided no further detail about the nature of the claims.
The Labour Party launched its investigation into Mr Lewis after a party member told the Independent newspaper that he had groped her.
Mr Lewis told the BBC he was “vigorously” disputing the allegation, which he said he had been “pretty taken aback” by.
“I don’t as a rule at packed Labour party conferences grope people’s bottoms when I greet them,” he said.
“It’s just not how I roll, it’s not what I do.
“Is the person mistaken? Have I given them a hug and this has been misinterpreted? I don’t know.
“All I know is that I would not deliberately do that, do what’s alleged. I completely deny that.”
Luton North MP Mr Hopkins has also denied sexual harassment after party activist Ava Etemadzadeh, 27, told the BBC that he had hugged her inappropriately after a student event in 2014.
Mr Hopkins said he had given her a “brief, sleight hug just before getting into my car”.
He was suspended by the party on Thursday while an investigation takes place.
And Labour’s former foreign office minister, Ivan Lewis, has denied claims he made non-consensual sexual advances towards women.
Buzzfeed News reported that a woman alleged he had touched her leg and invited her to his house at a Labour Party event in 2010 when she was 19.
Mr Lewis said in a statement to the website that he had “never made non-consensual sexual comments or sexual advances to women”.
He added: “However, I understand that a few women have claimed that my behaviour made them feel uncomfortable.
“I have on occasion asked women I work with out for drinks or dinner, or developed strong feelings for them, and I am genuinely sorry if this was unwelcome or inappropriate in the circumstances, and caused anyone to feel awkward.”
Prime Minister Theresa May is due to meet opposition party leaders, including Jeremy Corbyn, on Monday to discuss proposals to bring forward a new grievance system for Westminster staff and MPs.
The Conservatives have published a new code of conduct for their MPs and other elected representatives in the wake of sexual harassment allegations.
Meanwhile, it was announced that Labour would appoint an independent specialist organisation to offer advice and support to individuals affected by sexual harassment in the party.
Labour also said the independent legal expert, Karon Monaghan QC, would investigate party activist Bex Bailey’s allegations.
Ms Bailey has said she was raped at a party event and a senior Labour official discouraged her from reporting the attack.
She said she was told reporting the alleged 2011 incident could “damage” her and that she was given no advice on what she should do next.