Mr Woolgar, who took over the job in September 2001, quit and said "it was time to move on".

The trust's director of nursing, Julie Burgess, will take up the role on a temporary basis.

Chairwoman of the trust Professor Phyllida Parsloe said: "It was his decision to resign and so of course although I understand the reasons, they are his reasons not mine.

"He has come into an immensely difficult situation with huge pressure on the hospital and with an increasing number of emergencies and a serious bed shortage.

"He has brought energy and has worked very hard indeed but now he feels it's time to move on."

Tony Woolgar joined the trust after a spell as chief executive of Pinderfields and Pontefract Hospitals NHS Trust in Yorkshire.

The trust oversees seven hospitals in the Bristol area, including Frenchay and Southmead.