Dr Reynolds, who steps down as Defra's chief veterinary officer after four years, has also faced a number of other animal health issues including bird flu and bluetongue outbreaks during her time in office.

The Environment Department (Defra) said her deputy, Dr Fred Landeg, would take over until a new appointment was made.

Dr Reynolds faced criticism over the decision to declare the country free of foot and mouth in September, just days before a secondary outbreak was discovered, but today she won plaudits for her work in animal health.

Environment Secretary Hilary Benn said: "I am extremely grateful for Debby's advice and hard work on behalf of the Department both during the recent animal disease outbreaks and over the years. I wish her all the very best in her future career."

Announcing her retirement, Dr Reynolds said: "I have been the Chief Veterinary Officer for nearly four years and I am immensely proud of the work that we have carried out.

"The events of this summer were the true test of our contingency planning and the partnership work we have established - we have built a disease control strategy which is the best in the world."

Before taking over from Jim Scudamore as chief vet four years ago, Dr Reynolds was veterinary director at the Food Standards Agency.

In her early career, she was a veterinary research officer at the Institute of Animal Health. She joined the State Veterinary Service in 1984, working in the Veterinary Investigation Service until 1991 and at the Ministry of Agriculture, Fisheries and Food (Maff) until 1994.

She was then head of the bacteriology department at the Veterinary Laboratories Agency from 1994-97, before becoming Maff's head of endemic animal disease and zoonoses until she took up her appointment at the Food Standards Agency in 2001.