Sir Liam Donaldson will resign as Chief Medical Officer in May next year after 12 years of service, after original plans for his retirement earlier this year were put on hold amid the potential swine flu crisis.

The 15th CMO since the role was created back in 1855 to help focus efforts against cholera epidemics, Sir Liam is credited with leading the charge for many aspects of National Health Service reform and driving improvements to public health.

According to the DH, his work and recommendations have led to a whole host of different initiatives and policies that have benefited the general public and paved the way for better health, including: smoke free public and work places; the establishment of the Health Protection Agency and the National Patient Safety Agency; and the introduction of clinical governance in the NHS, to name but a few.

Sir Liam, who is also chair of the Pandemic Influenza Programme Board, had already once put his plans to retire - on turning 60 in mid-2009 - on hold in order to lead the response to the swine flu pandemic, and has said he will do so again should the current pandemic unexpectantly worsen.

Prime Minister Gordon Brown thanked sir Liam for his “outstanding work” as CMO since 1998. “He has made an extraordinary contribution to the nation's health, from championing the ban on smoking in public places, to tackling the shortage of donated organs and most recently leading our response to the swine flu pandemic”, he said, and added that “his leadership and action in these areas and others will have saved many, many lives”.

Others were equally praising of Sir Liam’s achievements. Health Secretary Andy Burham noted that he has “brought courage and foresight to the role of improving the nation's health”, that “his leadership and reassurance have taken the NHS and the country through a challenging year, and his preparations for this moment over many years put us in the best position to deal with it”, while NHS Confederation chair Bryan Stoten claimed: “It is no exaggeration at all to say that there are people alive today who would not have been had it not been for Sir Liam’s work”.

Plans for his successor will be announced at a later date, the Department of Health said.