Faith schools should be legally obliged to teach that homosexuality is "normal and harmless", and gay civil partnerships should be replaced by true marriage, Nick Clegg said last night.

In a pitch for the gay vote unprecedented in its scope, ahead of a general election likely in May, the leader of the Liberal Democrats threw down the gauntlet to his opponents. He called on the Tories, and in particular the Conservative leader David Cameron, who has voted against gay rights, to prove that they really supported full gay equality.

In an interview with The Independent columnist Johann Hari for today's edition of Attitude magazine, Mr Clegg changed the terms of political debate on what it means to be gay in Britain. The father-of-three detailed a series of proposals, among them:

* Force all schools – including faith schools – to implement anti-homophobia bullying policies and teach that homosexuality is "normal and harmless".

* Change the law to allow gay men and women the same marital rights as straight couples, including the symbolic right to use the word "marriage" rather than civil partnerships.

* Reverse the ban on gay men being allowed to give blood.

* Guarantee any refugees genuinely fleeing a country because of persecution over their sexual orientation asylum in the UK.

* Review Uganda's membership of the Commonwealth if its government was to bring in the death penalty for practicing gays.

Mr Clegg launched a withering attack on the Tories, describing David Cameron as someone who is “very difficult to trust” on the issue of gay rights. His claim reflects an important battle between the Lib Dems and the Tories for the votes of liberal-minded voters in general, as well as the gay community.

The Lib Dem leader complimented Labour for its track record on gay rights, which has included the introduction of civil partnerships, the equalisation of the age of consent and the repeal of Section 28, which forbode local authorities and schools from “promoting” homosexuality. But more must be done, he said, to make Britain a place where homosexuality was no longer discriminated against.

But he denounced Mr Cameron. “He’s a confection,” said Mr Clegg. “I don’t really know what he believes in. I don’t know what his convictions are and the reason is because they keep changing – and they seem to change for convenience. So when it mattered, when people went through the lobby to vote on Section 28, his convictions were on the wrong side. Suddenly they’ve changed and we get an apology!”

Mr Clegg questioned the Tory leader’s record of supporting gay equality, highlighting how Mr Cameron voted against the repeal of Section 28 (he last year apologised for the Tories’ introduction of Section 28) and how he has allied his party with right-wing anti-gay groups in Europes.

“The surveys of a lot of the next generation of Conservative MPs show massive residue of indifference at best, prejudice at worst,” said Mr Clegg.

In his new year message, Mr Cameron pitched for the support of natural Lib Dems by declaring that there was a “lot less disagreement than there used to be” between the two opposition parties. He was rebuffed by Mr Clegg, who sensed an attempt to hoover up Lib Dem votes.

Allies of Mr Cameron last night rejected Mr Clegg’s criticisms. They insisted that the Tory leader was not an opportunist, pointing out he apologised for his mistake on Section 28 when he ran for the Tory leadership in 2005 – not on the eve of this year's general election. “David feels passionately about this issue,” one aide said.

A Tory Government would include civil partnerships when it implemented its plans to change the tax system to reward marriage. However, the Tories are unlikely to give full marital rights to gay couples.

If they win the election, the Tories might reverse the ban on gay men being allowed to give blood but are not expected to force faith schools to teach that homosexuality is normal or guarantee asylum to refugees fleeing because of persecution over their sexuality.

In his first speech to the Tories’ annual conference as party leader, Mr Cameron won applause after stating his support for civil partnerships.

Mr Clegg’s comments on marriage and faith schools will anger many religious communities and organisations.

A recent study by the gay rights group Stonewall found that bullying of gay pupils rose significantly in faith schools. Asked whether the Lib Dems would make it a legal requirement for schools, including faith schools, to teach that homosexuality is normal and harmless, he replied: “Yes – and crucially faith schools should have a requirement to have an anti-homophobic bullying policy at their school.”

But speaking to The Independent last night, one senior Anglican bishop (who asked not to be named) said: “I think this will go down badly even among the not overtly evangelical. Instituting something that must be taught, come what may, is frighteningly fascist.”

The Rev Janina Ainsworth, chief education officer for the Church of England, said she saw no reason why the current laws governing sex education in schools should change. “The Church’s traditional teaching is that sex should be set within the framework of a faithful marriage, and sex education in church schools will be delivered within that context,” she said. “At the appropriate stage within the sex education curriculum, all students, in all schools, should have the opportunity to examine the full range of views on different aspects of sex and sexuality, and to develop their own considered position. Further upheaval of the guidance for sex education would not be welcomed by many schools, church or otherwise.”

On marriage rights the Lib Dem leader also took the most openly progressive stance of the three main parties. The current Labour government introduced civil partnerships in 2004 but stopped short of allowing gay couples to call themselves married because of a backlash from religious leaders.

But last night Mr Clegg asked: “If we don’t want to discriminate, why do we make differences in language? Language is a hugely important signifier of how we segment society and how you seek to create differences between people. Since we don’t want to make differences on this and the law has moved a great deal to do that, we should be linguistically the same too.”

On asylum seekers – an issue which is notoriously unpopular with the electorate – Mr Clegg was equally bullish, describing Britain’s asylum system as “the most inhumane, irrational, cruel systems imaginable”.

“It’s a moral stain on our collective consciousnesses,” he said. “The public debate has transformed asylum seekers into threats rather than human beings.”

He said Lib Dem policy would be that Britain should provide sanctuary to those fleeing persecution because of their sexual orientation: “It’s not just me that says this, it’s international law that says it.”

Ben Summerskill, chief executive of the gay rights group Stonewall, welcomed Mr Clegg’s comments but added that he believed Mr Cameron had genuinely changed his views on gay rights.

“Nick Clegg has always been very supportive and intuitive when it comes to gay rights, but I do believe Cameron is also committed, not least because being supportive to gay people is now integral to becoming a modern, electable 21st-century party,” he said. “The fact is that any politician nowadays who twitches at the mention of homosexuality will have difficulty connecting with a voter under the age of 35.”

Gay rights: From Henry VIII to New Labour

1533 Henry VIII, a monarch not renowned for his celibacy, passes the Buggery Act, which makes anal intercourse an offence punishable by hanging, regardless of gender. The practice continues apace.

1861 The death penalty is removed, but anal sex remains an offence punishable with imprisonment. By 1885 the laws are expanded to prohibit sex between two men – it did not occur to the Victorians to legislate against sex between women.

1950s A number of high-profile homosexual men – including the wartime code breaker Alan Turing – are outed and prosecuted because of their sexual orientation. Turing later committed suicide. The government conducts a series of reports into gay equality and behaviour.

1967 The Sexual Offences Bill effectively decriminalises homosexuality, but the age of consent remains at 21 for gay men. Widespread social acceptance remains far off.

1988 The gay rights movement suffers a setback when a Tory-led Parliament passes Section 28, a by-law banning the "promotion" of homosexuality in local authorities and schools.

1994 The age of consent for gay sex is lowered to 18, and finally lowered to 16 in 2000.

2002 Section 28 is finally repealed despite opposition from the Conservatives. David Cameron votes to keep it. The same year, gay couples are given equal rights to adopt.

2004 Gay couples are allowed to wed in civil partnerships, but Labour stops short of allowing full marriage.