This is the text of a message from the departing Trust chairman, Sir Michael Lyons:

As I come to the end of my four-year term as Chairman of the BBC, I want to send a message of thanks and support to everyone who has played a part in helping to deliver the BBC's services over that period.

I know that goes well beyond those who work directly for the Corporation and now involves a large and complex network of skills and talents.

Earlier this month the International Herald Tribune published an article suggesting that the BBC faced a difficult and uncertain future, and there are certainly continuing challenges ahead.

Nonetheless, I am optimistic about the BBC's health and future prospects for continuing to play its keystone role in the economic, social and cultural life of the UK. Indeed, I believe that this has been strengthened by the work of the last four years.

Both parts of the BBC - Trust and executive - have worked closely together to shape a new strategy (Putting Quality First) and the Delivering Quality First exercise is now beginning to map out the way in which that can be implemented with the resources available.

The BBC now has an agreed emphasis on serving all audiences; striving to produce more distinctive content; reducing overhead costs and focusing intently on value for money. These, together with the ambition to become a more open, more collaborative organisation, address the two pillars essential to support the BBC's health: continuing public support and positive relations with other parts of the communications industry.

There is more to be done on all fronts and further refinements to make in the way we work together. Nonetheless, the strength of our current position is clear to see with record levels of public affection and trust; services which reach virtually every household and improving quality of programmes.

The last four years have not themselves been short on challenge but I think we are the stronger for that. Thank you for your contribution and let me particularly thank the many of you who I have met, in the course of our work together, for the courtesy, enthusiasm and straight speaking that I have invariably experienced.