Prince Charles's accession to the throne will provide a 'particularly opportune moment' to make the case for disestablishment of the Church of England, according to a report published today by the National Secular Society.

Debate about a separation between church and state – seen by some as potentially beneficial to both sides – is regarded as off-limits while the Queen remains monarch.

But the new report, called Separating Church and State: The Case for Disestablishment, questions the institutional links between Church, Monarchy and Parliament and indicates that secularists are gearing up for a major discussion about the issue when Prince Charles accedes to the throne.

The report points out that only 25 per cent of countries had a state religion in 2011, while, of those, a minority were classed as liberal democracies, and that only Britain and Iran have religious leaders in their legislatures by right.

Twenty-six CofE bishops currently have reserved seats in the House of Lords, with the right to debate and vote on changes to the law.

Meanwhile, the CofE retains a key role in the coronation of a monarch, who is crowned and anointed by the Archbishop of Canterbury in an Anglican ceremony at Westminster Abbey.

The reigning monarch remains head of the Church, holding the titles of supreme governor of the Church of England and Defender of the Faith.

The report says: 'The wording of the coronation oath, which implies that anyone not sharing the beliefs promulgated at the service are not to be included as full citizens of the state, does little, for an event that is supposed to unite the nation, to suggest any kind of inclusivity.'

The report claims Prince Charles wishes to assume the title 'Defender of Faith, as opposed to 'the faith'. It says the traditional title 'will be antagonistic for the non-Anglican majority of the UK population. On the other hand, attempting to avoid this difficulty by adopting the title 'Defender of Faith' will antagonise many supporters of the Church of England'.

Other elements of an established Church include the formal appointment by the monarch of bishops and archbishops; the formal approval by Parliament and the requirement of royal assent to changes to Church law; and the saying of Anglican prayers at the opening of daily business in both houses of Parliament.

The report highlights what it calls the Church's 'regressive' stance on moral issues. Citing gender rights, same sex marriage and assisted suicide, it says: 'The claim that the Church of England offers a unique source of moral guidance clashes sharply with the regressive stance taken by church leaders on a range of moral issues, and establishment allows them a privileged position in parliament through which they can try to impose these views on others. It is simply absurd to imagine that religious leaders have access to a wellspring of ethical knowledge that is somehow denied to non-religious citizens.'

The report adds: 'The notion that a state religion is required to uphold a sense of national cohesion is clearly anachronistic in a multi- and non-faith democratic society, and it is simply impossible for the church to speak for, let alone actively represent, the multiplicity of faiths and beliefs in modern Britain today (especially since the largest single belief group is now the non-religious). Establishment, by definition, grants undue privileges to one particular religion, to one particular section of the population and to one particular institution.'

The report acknowledges that there is 'no clamour' for disestablishment among politicians and that most members of the public are 'simply indifferent to the issue'.

However, it says that overt support for establishment is 'weak' and it notes that the Church in Wales and Ireland has already been successfully disestablished.

Rowan Williams, the former Archbishop of Canterbury, has said that it would be 'by no means the end of the world if Establishment disappears' though he has made it clear he does not support it at this time.

The report suggests that one way forward could be 'a process of gradual dismantling rather than securing a single clean break'.

It concludes: 'The voices of religious privilege are loud and their vested interests are strong. But if the problems of the 21st century life are to be effectively addressed, and if Britain is to become a modern state rather than one in which parliament continues to cleave to its medieval past, then the separation of church and state needs to be part of the solution.'