* PM's "secularist" approach hits church-state ties-Carey
* Cameron has alienated some traditional voters
* Downing Street says backs Christianity
British Prime Minister David Cameron is alienating Christians by promoting gay marriage, an influential former leader of the world's 80 million Anglicans said on Saturday.
In a strongly worded article, former Archbishop of Canterbury George Carey said Cameron's plan to legalise gay unions hid an "aggressive secularist" approach that threatened the link between church and state.
The comments echoed widespread concern about the policy among some Christians - and also highlighted the challenge facing Cameron whose efforts to modernise his centre-right Conservative Party have antagonised some traditional party voters.
"The danger I believe that the government is courting with its approach both to marriage and religious freedom, is the alienation of a large minority of people who only a few years ago would have been considered pillars of society," Carey wrote in Britain's Daily Mail newspaper.
Carey's comments come at a bad time for Cameron, who as the economy flounders is attempting to woo right-leaning voters with tough talk on immigration and the European Union.
The former Anglican leader also condemned what he saw as a lack of government support for Christians who choose to wear a cross at work, a practice that has been challenged in the past due to rules on religious expression at the workplace.
He cited a survey by pollster ComRes saying more than two thirds of Christians in Britain felt they were a "persecuted minority" and that more than half who voted Conservative in 2010 would not do so in 2015.
"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," Carey said.
Cameron's Downing Street office rejected Carey's accusations, and praised the church's role in charities and education, but did not address the issue of gay marriage.
"This government strongly backs faith and Christianity in particular, including backing the rights of people wanting to wear crosses at work and hold prayers at council meetings," Downing Street said in a statement.
"The prime minister values the profound contribution that Christianity has made and continues to make to the country, which is why he strongly backs it," the statement continued.
Carey was Archbishop of Canterbury from 1991 to 2002. Current Archbishop Justin Welby this month said some gay relationships were "stunning" in quality, but he is also opposed to gay marriage.
As elsewhere in Europe, the number of regular churchgoers in Britain has been declining in recent decades.