William Shakespeare's former parish church has threatened to split from the Church of England if the next Bishop of London takes a liberal stance on sexuality.

St Helen's Bishopsgate is one of the British capital's largest and most historic churches, whose congregation is worried about who will be appointed to replace Lord Chartres, who retires as bishop this year.

The church's rector Rev William Taylor told the faithful in a service that the new bishop who will be announced in the New Year will have to deal with the question of whether to "declare as sin what God calls sin".

If he or she does not condemn homosexual relationships then a split from the C of E would be "unavoidable", he said.

"We now wait to see what the new Bishop of London's views are," he said according to Christian news outlet Premier.

"My first question to him or her will be: 'Are you prepared to openly to declare as sin what God calls sin and to summon all people to repentance and to do so publicly?'

"If the answer is 'no' then there is an 'unavoidable avoidance' for us all."

The Bishop of London is one of the five most senior roles in the Church of England, along with the archbishops of Canterbury and York and the bishops of Durham and Winchester.

The new appointment comes as the church grapples with controversial issues such as conducting same-sex marriages and female clergy members. The Times reported that the Bishop of Chelmsford, Stephen Cottrell, is one of the front-runners.

He has called for services of "thanksgiving" to bless same-sex marriages, but not backed performing same-sex weddings.

St Helen's Bishopsgate is a large evangelical church with around 2,000 worshippers. It is said to be the local parish of Shakespeare, when the bard lived in the area around 1590.

In July this year, the General Synod, Church of England's governing body, made a historic move to welcome transgender people.