Christopher Bland: It's an impossible job. And also the best job in world broadcasting

The DG will have to stand upfor public-service broadcasting and defend the BBC's independence

The moment Lord Patten, the Chairman of the BBC Trust, announced he was appointing head-hunters to advise the BBC "on what sort of person we should be looking for" as the next Director-General, the genie was out of the bottle. Mark Thompson's announcement that he would step down in the autumn simply confirmed the process had begun.

It is a difficult process to control. Lord Patten and the trustees will try to keep it confidential, and will almost certainly fail. When I and the board of governors selected the next DG in 1999, we went to extraordinary lengths to keep the candidates' identities secret. We were not aided by the candidates, several of whom lobbied individual governors and the press quite shamelessly, as did at least two senior members of the BBC executive. One candidate, Andrew Neil, wrote an account of his interview for The Sunday Times only days after it had taken place.

The bookmakers are already having a field day. No doubt it will be possible to take out doubles on the Archbishop of Canterbury and the DG. The Trust and the candidates can look forward to a torrid six months before the white smoke rises above Broadcasting House.

Lord Patten will do well if he can persuade the trustees that the selection job should be delegated to a four- or five-strong panel. I tried and failed in 1999 – understandably, as the selection of the DG is the most important single decision in the life of the BBC. Whatever the size of the panel, relying on the interview process is notoriously ineffective. The best guide is the recent track record of the applicant, together with references taken out in person.

Mark Thompson's view on the candidates will be worth hearing. He has done a good job during the past eight years, well supported by a strong team. He has obeyed the first requirement, which is to survive, something his predecessor, Greg Dyke, for all his charisma, did not.

Mark has done more than simply survive. He has negotiated a reasonable licence fee deal. He has moved staff kicking and screaming out of London, cut costs, and accepted that the world will not come to an end if the Grand National moves to Channel 4. He has dealt with the BBC's inevitable errors of judgement with speed and authority. Above all, he has allowed creativity to flourish, and the BBC remains the best broadcaster in the world.

His successor will need to show she can recognise creative talent when she sees it. [I cannot say he/she throughout this piece; there has never been a woman DG or chairman, and it would be magnificent if a woman turned out to be the best candidate]. She will have to understand the unique position of the BBC in the broadcasting ecology of the UK. She will have to stand up for public-service broadcasting, defend the BBC's editorial independence, and admit mistakes when they are made.

The next DG will have to develop an effective relationship with Lord Patten and the Trust, and make sure both sides know the difference between strategy (the Trust) and day-to-day operations (the DG). The DG is currently chair of the executive committee, and is likely to remain so, although this is not a model that should survive the next Charter Review. She will have to develop a working relationship with both Houses of Parliament, survive onslaughts from the Murdoch press and the Daily Mail, and cultivate allies wherever she can find them.

It is an important job, an impossible job, and the best broadcasting job in the world. I wish her [or him] the best of luck.

Sir Christopher Bland was chairman of the BBC Board of Governors from 1996 to 2001.