Archbishop John Sentamu of York is an early favourite among candidates to succeed Rowan Williams as Archbishop of Canterbury but his selection is not a foregone conclusion.

Dr Sentamu, 62, is a year older than Dr Williams who announced on Friday that he is quitting the post he held for a decade to become Master of Magdalene College in Cambridge.

The move is no great surprise. Rumours have been circulating for months of already agreed engagements in Cambridge. One of Dr Williams' major considerations concerns the next international Lambeth Conference of Bishops, scheduled for 2018.

Having decided some time ago he would not to take the helm for it, he needed to give a successor time to plan it well. Moreover he is of an age where he could make a viable new career as an academic, an option perhaps more fitted to his personal gifts.

Archbishop Robert Runcie, Archbishop from 1980-91, was fond of saying that whereas one of his historic predecessors, St Alphege, was beaten to death with ox bones by invading Vikings, "I often feel I'm being beaten to death by the press." More than one Archbishop of Canterbury was martyred. While this has not happened with Dr Williams, his incumbency has been a painful one.

Simply put, the job of the Archbishop is to be a parson of the nation, servant of the servants of One who humbly washed feet, gave voice to the poor, and offered a vision for what life would be like with God in charge. It is a political role as well and inevitably this makes an Archbishop the target of brickbats, even when not deserved.

Dr Williams has had more than his fair share of political spats: issues such as Sharia Law, global warming, the legality of the Iraq war, and the morality of the killing of Osama bin Laden. In addition he inherited deep divisions within world Anglicanism over sexual morality, a debate now even more complex with the UK government’s decision to push ahead with same-sex marriage legislation.

For his part Dr Williams believes the global Anglican problem is about how to make decisions when people hold strongly different views. He feels disappointment that so much of his time as Archbishop had to be devoted to crisis management. He is not convinced that everyone genuinely wants to see rifts within Anglicanism overcome.

His proposed solution is an Anglican Covenant which spells out in very accessible terms what is the ethos of Anglicanism, and tries to offer principles for consultation over divisive issues. The strongest opposition to the Anglican Covenant seems to be in the Church of England. The odds are that he will leave office with his church having rejected the Covenant.

There will not be a long interregnum. The government will shortly appoint a layperson to chair a nomination committee, with 16 members. Their task will be to place two names in priority order before the Prime Minister who in turn sends his preferred choice to the Queen.

Even though Prime Minister David Cameron supports gay marriage, he has stated he will not insist on the appointment of someone sharing his view. In the normal run of things it might be expected that since Rowan Williams represented a liberal Catholic position it is now the turn of the evangelicals. However insiders observe that a recent casual vacancy was filled by a liberal Catholic replacing an evangelical. That might prove crucial.

As well as Dr Sentamu names being mentioned as possible candidates include Richard Chartres (London), Christopher Cocksworth (Coventry), Nick Baines (Bradford), Tim Stevens (Leicester) and Stephen Cottrell (Chelmsford). In fact the field is wide open. Certainly no successor will match the intellect of Dr Williams.

Dr Williams has exercised his responsibilities with great grace in very difficult circumstances. AN Wilson, literary critic, has summed up the situation up well: “The Church of England did not deserve him.” As happens with Archbishops of Canterbury, the quality of their contribution often only comes to light in hindsight.

John Martin is a journalist, commentator and UK & Europe Director for Middle East Media