UK Transport Secretary Resigns

She will step down at the next Cabinet reshuffle, which could come as soon as next week.

Miss Kelly's departure threatens to overshadow Mr Brown's attempts to shore up his leadership with a defiant Labour conference speech.

She is understood to have had serious doubts about Mr Brown's leadership, and her decision to quit has reignited speculation about the Prime Minister's future.

However a source close to Miss Kelly inisted her decision was made on purely on personal grounds, telling reporters she "thought the time had come to spend more time with her four young children."