The senior peer Lord Lester of Herne Hill is facing a record suspension from the House of Lords after he was found to have sexually harassed a woman in the course of his parliamentary duties.

The Lords Privileges and Conduct Committee recommended he should be suspended until June 2022 after offering the complainant “corrupt inducements” to sleep with him.

Peers are expect to vote on Thursday whether to accept the committee’s recommended punishment, which would be the longest suspension in modern parliamentary history.

In a statement, Lord Lester flatly rejected the committee’s findings, saying the allegations against him were “completely untrue” and that he had produced evidence clearly demonstrating the alleged events did not take place.

The finding follows an investigation by the Lords Commissioner for Standards Lucy Scott-Moncrieff after the woman – who has not been identified – complained the peer had breached the Lord’s Code of Conduct.

In its report the committee said: “We endorse the conclusion of the commissioner that in respect of that conduct Lord Lester of Herne Hill breached provisions of the code in failing to act on his personal honour by sexually harassing the complainant and offering her corrupt inducements to sleep with him.”

In his statement, the peer said: “These allegations are completely untrue. I produced evidence which clearly demonstrated that what I was said to have done 12 years ago did not happen.

“Independent counsel who previously advised the committee on its procedures provided an advice which concluded that the investigation was flawed. I regret the committee’s conclusions in the light of these materials.

“There has to be a fair process for investigating sexual harassment claims in Parliament. Parliament is supposed to be a bastion of the rule of law but has ignored calls to reform this procedure properly for 20 years.

“I hope to be judged by my work over decades for gender equality, race relations and free speech.”

Prominent QC Lord Lester, 82, announced in February he was stepping down as a Liberal Democrat spokesman on human rights and withdrawing from the party whip following the complaint.

In her report to the committee, Ms Scott-Moncrieff rejected Lord Lester’s challenge to the finding, saying the complainant and her witnesses presented “strong and cogent evidence”.

A subsequent report by the sub-committee on Lords’ conduct found his actions constituted a “grave abuse of power” and recommended he should be expelled altogether.

However the main Privileges and Conduct Committee accepted that, at the time the behaviour which led to the finding took place, there was no power of expulsion and recommended it should be substituted with a term of suspension.

In recommending a suspension to June 3, 2022 – past the due date of the next general election – the committee said it had taken into account the length of previous suspensions as well as the seriousness of the case.

“Lord Lester made a dishonourable promise backed by a dishonourable threat,” it said.

According to her statement to the commissioner, the complainant said Lord Lester had told her if he slept with her he would make her a baroness “within a year” but if she refused he would ensure she never had a seat in the Lords.

The woman – who is said to be well-known to government as an expert in her field – said she first came to meet the peer during the course of work relating to parliamentary business in her field of expertise.

She said that after she missed her train following a meeting in the House of Lords, Lord Lester had suggested she should stay the night with him and his wife at their London home.

On the drive to the house she said the peer had put his hand “very firmly” on her thigh and despite her protests had “continued to grope my thigh for the length of the journey”.

The next morning, after his wife had left, she said the peer had come up behind her and put his arms around her and when she pushed him away he had pursued her around the kitchen.

Not long afterwards, when she was attending another meeting in the Lords, she said he had made the offer to make her a peer if she slept with him.

“He said that if I was a ‘good girl’ and did what he was asking, I would be in the House of Lords and could visit his house abroad with him,” she told the commissioner.

“He made a number of further inappropriate sexual comments to me such as that he could see me becoming a demanding mistress. I was distressed and shocked by his behaviour.”

She said that she had not made a complaint at the time as she did not think she would be believed and that her word against that of Lord Lester was “not an equal contest”.

Lord Lester told the commissioner that while he recalled the woman coming to stay with him and his wife after she missed her train, he denied groping her thigh or making other sexual advances.

He had no recollection of any conversation with her in which he spoke of matters of a sexual nature and categorically denied making an offer of a peerage or threatening the woman if she refused to sleep with him.