Former Archbishop of Canterbury Lord Carey has launched a scathing attack on Prime Minister David Cameron.
In an article for the Daily Mail, Lord Carey says many Christians doubt the PM's "sincerity" when he pledges to protect their religious freedoms and accuses ministers of "aiding and abetting" discrimination against believers.
He points to Government plans to legalise gay marriage as evidence of an "aggressive secularist and relativist approach" and argues that Mr Cameron has fed Christian "anxieties" more than "any other recent political leader".
Lord Carey also says a new poll suggesting that more than two-thirds of Christians feel they are now part of a "persecuted minority" shows the Government must do more to demonstrate its commitment to stand up for faith.
The ComRes poll commissioned by the Coalition for Marriage also found more than half of Christians who backed the Conservatives in 2010 say they will "definitely not" vote for the party in 2015.
Lord Carey expresses alarm about Labour MP Chris Bryant's campaign to turn the 700-year-old Parliamentary chapel of St Mary Undercroft into a multi-faith prayer room so that gay couples can get married there.
But he also directly calls into question the Prime Minister's actions, saying: "I like David Cameron and believe he is genuinely sincere in his desire to make Britain a generous nation where we care for one another and where people of faith may exercise their beliefs fully.
"But it was a bit rich to hear that the Prime Minister has told religious leaders that they should 'stand up and oppose aggressive secularisation' when it seems that his Government is aiding and abetting this aggression every step of the way.
"At his pre-Easter Downing Street reception for faith leaders, he said that he supported Christians' right to practise their faith. Yet many Christians doubt his sincerity.
"According to a new ComRes poll more than two thirds of Christians feel that they are part of a 'persecuted minority'. Their fears may be exaggerated because few in the UK are actually persecuted, but the Prime Minister has done more than any other recent political leader to feed these anxieties.
"He seems to have forgotten in spite of his oft-repeated support for the right of Christians to wear the cross, that lawyers acting for the coalition argued only months ago in the Strasbourg court that those sacked for wearing a cross against their employer's wishes should simply get another job."
The new poll suggests continuing resentment over legalising same-sex unions, even though there is special protection for the Church of England in the law, and Lord Carey's successor Justin Welby has softened the Church's stance on the issue.
Two thirds of those polled said they believed allowing same sex unions was an attempt to make the Conservative Party look trendy.
The poll comes after a series of controversial cases between Christians and employers over their rights to express their faith in the workplace.
Recent cases include Adrian Smith, a Trafford housing manager who says he was demoted and had his pay docked 40% after questioning the Government's plans for same sex marriage and Reverend Brian Ross who was sacked as the Chaplain of Strathclyde Police, apparently because his support for traditional marriage did not fit with the force's equality and diversity policies.
In another case, graphic designer Jamie Haxby is suing a hotel after claiming he was turned down for a job because he is a Christian.
Communities Secretary Eric Pickles insists that unlike New Labour 'we do do God' and has agreed freedom of religion has been undermined.
He has vowed to change the law if necessary to stop people being taken to task for wearing a cross or a rosary, and says council should not try to ban prayers before meetings.
But the march of secularism means Britain will no longer be a Christian country within just 20 years, according to official research by the House of Commons library.