The National Secular Society has written to Bideford Council to say that its prayers at council meetings are “illegal”.

It has threatened the council with a judicial review unless it stops the prayers and hopes the action will “set a precedent that will affect the many other councils that have prayers as part of their agenda”, the NSS said on its website.

The NSS has decided to take action in response to a complaint from local councillor Clive Bone, whose motions to remove prayers from meeting agendas have failed.

The former Archbishop of Canterbury, Lord Carey, defended council meeting prayers and said they should only be ended through a vote by councillors.

He told the Guardian: “The centuries-long tradition of saying of prayers before council meetings is simply an acknowledgment of the important role the Christian faith plays in civic life.

“The attempt to rule such prayers as discriminatory is an attack on freedom and a cynical manoeuvre to drive public expressions of faith from national as well as local life.

“This should not be a matter for the courts as it concerns democratic freedoms. Councillors can halt the practice of saying prayers through a vote rather than resorting to judicial means.”

Keith Porteous Wood, executive director of the NSS, said: “We have no objection to people praying if they want to – but it should not form an integral part of the Council meeting.”

He added: “The council should confine itself to providing services for the public, not forcing religious services on its councillors. We are a secularist organisation, and as such we seek to separate politics from religion. Council prayers represent a fusion of politics and religion and a completely unnecessary one.”