A former Archbishop of Canterbury has railed against the prime minister’s support of equal marriage rights for gay couples, calling it undemocratic and ‘one of the greatest political power grabs in history’.

Writing in the Daily Mail, Lord Carey said marriage was not ‘owned’ by the state or any religion but pre-dated both as a cultural institution.

As a result, he argued, no one should be allowed to alter it.

He was pledging his support for a new Coalition for Marriage, which has been created to oppose marriage equality efforts.

Lord Carey writes at length about the importance of the marriage relationship for society and speaks of his own wife’s long support of him.

But he argues that gay should not be able to marry because equality does not “mean being the same”.

Instead, he recommends the two institutions of marriage and civil partnerships be maintained.

Lord Carey also attributes the growing support for marriage equality to “pressure groups and image advisers” rather than the general public.

Allowing gay couples to marry, he adds, would change the institution “beyond all recognition”.

Schools, he writes, “will be forced to teach children the new definition of marriage – which will run counter to the wishes of many parents”.

He adds that cases like that of Peter and Hazelmary Bull, who lost their appeal after being sued for discrimination because they refused two male civil partners a shared room in their hotel, were the “thin end of the wedge”.

The Archbishop of York Dr John Sentamu equated David Cameron’s support of gay marriage with the actions of a dictator earlier this year.

As a result, a protest was held outside his cathedral, York Minster, and Sentamu, who was born in Uganda, received a slew of racist emails.

The Coalition for Marriage hosts a petition on its website opposing “any attempt to redefine” marriage.

Signatories include Lord Carey, Conservative and Labour MPs, the director of the Christian Institute. There were 230 signatories in total at the time of publication.