The chair of the BBC Trust, Lord Patten, is resigning from his position immediately on health grounds after undergoing major heart surgery.
The former Conservative minister was admitted to hospital at the end of April with severe chest pains before having a combination of bypass surgery and an angioplasty.
In a statement Lord Patten said his doctors had advised him to "reduce the range of roles" he takes on.
On stepping down from the BBC Trust, he said:
"This is a position that requires and has received from me 100 per cent commitment, and has been my priority at all times.
"It would not be fair to my family to continue as before; and equally it would not be fair to the BBC and those it serves not to be able to give that commitment which the role demands."