He was speaking at a hustings organised by gay rights charity Stonewall. More than 500 people were present to hear from the four main mayoral candidates.
Labour candidate Ken Livingstone said London was "gay-friendly" but a lot more needed to be done.
Conservative Mayor Boris Johnson promised to bring out a gay manifesto ahead of the elections.
There are 350,000 voters from the LGBT (lesbian, gay, bisexual and transgender) community.
Mr Paddick said: "When I was in school I remember being manhandled, about to be thrown into a freezing pool of water fully clothed because I was gay, until a teacher intervened.
No Muslims ever came to me and said 'I want homosexuality banned'”
Mr Paddick, a former Metropolitan Police officer, said: "There needs to be an absolute culture change in the police. I will put that pressure on to deal with racism and homophobia within the police."
Livingstone told the crowd at the South Bank Centre that Muslims were now the target of prejudice which had previously been reserved for the gay community. "In 1906 the front page of the Daily Mail's headline was 'Jews bring crime and disease to Britain'.
"Then it was the blacks, then it was the Irish, then it was the lesbians and gays – there has always got to be an enemy. Rightwing politicians pander to bigotry."
Paddick, the Lib Dem candidate and former deputy commissioner of the Metropolitan police, said there needed to be a "culture of change" at Scotland Yard to eradicate prejudice.
He said: "A poll the other week showed that 20% of Londoners do not believe that the police are on their side and I think that proportion may even be higher because of the history that the LGBT [lesbian, gay, bisexual and transgender] community has had, particularly with laws which specifically discriminated against men and the enthusiasm with which the police enforced those laws.
"What I promise you is if I become the mayor and the crime commissioner on 3 May, I will put that pressure on to deal with racism and homophobia within the police."
On Friday, Johnson ordered his transport chiefs to pull the adverts booked by two conservative Anglican groups following outrage among gay campaigners and politicians saying that they were homophobic. The adverts, pulled just days before the posters were due to appear on buses in the capital, were booked on behalf of the Core Issues Trust whose leader, Mike Davidson, believes "homoerotic behaviour is sinful"