Mrs Browning, MP for Tiverton and Honiton, will leave her current position as Education and Disability spokeswoman at the next shadow cabinet re-shuffle, expected some time before the summer recess.

"I need to spend more time with my son who is not in good health and have decided to return to the backbenches. I am most grateful to William Hague for his kindness and understanding in this matter," she said.

Highly rated

A Conservative spokesman said: "It is genuinely a very sad business. Obviously, she is someone we rate highly but she has taken her decision and we respect that."

Mrs Browning, 51, who has two sons, was first elected in 1992 and just held onto her reshaped seat at the last election with a 1,653-vote majority.

She was a junior minister at the Ministry of Agriculture, Fisheries and Food between 1994 and the last election and was tipped as one of the Tory women most likely to shine in Mr Hague's new team.