(Britain's Queen Elizabeth (R) 'Exchanges the Peace' with the Archbishop of York John Sentamu (2nd L), watched by Prince Philip (REAR) and the Archbishop of Canterbury Rowan Williams, during the ninth Inauguration of the General Synod at Westminster Abbey, in central London November 23, 2010. REUTERS/Dan Kitwood)

Archbishop of Canterbury Rowan Williams, who has agonised about keeping his Anglican Communion from splitting over women and gay bishops and same-sex unions, announced unexpectedly on Friday that he would step down at the end of the year.

It was time to move on after a decade as archbishop, he said, and his new post as master of Magdelene College at Cambridge University would give him the time “which I have longed for” to think and write about the Church.

“I would hope that my successor has the constitution of an ox and the skin of a rhinoceros,” Williams said.

His resignation appeared to sound a death knell for his faltering project to forge more unity in the Anglican Communion, a federation of 38 national and regional churches representing 80 million Anglicans around the world.