A Tory MP has resigned from The Oxford Union in protest at its decision to invite two controversial figures to a free-speech event on Monday.
Dr Lewis resigned his life membership "with sadness"
Nick Griffin, leader of the British National Party (BNP) and David Irving - jailed for denying the Holocaust - were invited by the union debating society.
Shadow defence minister and MP for New Forest East Dr Julian Lewis said the students should be "ashamed".
The Oxford Union said it was important to give people of all views a platform.
Mr Griffin has repeatedly insisted the BNP is not a racist group.
'Couple of scoundrels'
He was convicted in 1998 for incitement to racial hatred for material denying the Holocaust.
Mr Irving was imprisoned for three years after pleading guilty to Holocaust denial in Austria.
In a letter to the union's officers and standing committee, Dr Lewis said he was resigning his life membership "with great sadness".
The MP, who studied at Balliol and St Antony's colleges, said the right to free speech should not guarantee access to privileged platforms.
"Nothing which happens in Monday's debate can possibly offset the boost you are giving to a couple of scoundrels who can put up with anything except being ignored," he said.
"It is sheer vanity on your part to imagine that any argument you deploy, or any vote you carry will succeed in causing them damage.
Nick Griffin and David Irving are due to speak at the Oxford Union
"They have been exposed and discredited time and again by people vastly more qualified than you in arenas hugely more suited to the task than an undergraduate talking-shop, however venerable."
Trevor Phillips, chair of the Commission for Equalities and Human Rights, told BBC1's Andrew Marr Show: "I think it is an absolute disgrace.
"As a former president of the National Union of Students I'm ashamed that this has happened.
"This is not a question of freedom of speech, this is a juvenile provocation."
The invitation has been opposed by the Oxford Student Union and the university's Muslim and Jewish societies.
However, on Friday the debating society voted by a margin of two to one to continue to extend the invitations to Mr Griffin and Mr Irving.
Hundreds of protesters are expected to gather at the university on Monday.
But Liberal Democrat MP Evan Harris, who is billed to speak at the forum, said it was the "views of these extremists which are a disgrace" and "not their right to hold their views".
"I have spent my whole political life opposing racism and bigotry, but it is vital to demonstrate that they will be defeated within our existing laws.
"The measure of our country's respect for free expression is our willingness to allow it for the most objectionable and offensive lawful speech, not just for those with whom we agree."
Simon Darby, BNP spokesman, described the expected protests as "very misguided".
"This event is a big breakthrough for our party to spread its message in democratic surroundings.
"It is ironic you have got people shouting 'fascism' while campaigning in the face of the process of democracy.
"Nick is looking forward to the event. It is easy to ignore the protests."