Twelve-year-old Georgina Horlick, diagnosed with the disease when aged two, died in Great Ormond Street Hospital on Friday.

Mrs Horlick said in a statement: "Georgie died from a lung infection six months after a bone marrow transplant, which was part of her treatment for leukaemia.

"The eldest of five children, she had originally contracted leukaemia at the age of almost three and had fought bravely through nine years of treatment.

"However she had a relapse last December and underwent the bone marrow transplant in May, which had left her particularly susceptible to illness."

Dr Alison Leiper, the associate specialist in paediatric oncology who was responsible for Georgina's day-to-day treatment, said: "Georgie Horlick was a remarkable little girl who bore her illness with a courage and determination of one much older than her short 12 years.

"We at the hospital all felt privileged to know her and enjoyed her mischievous sense of humour and witty intelligence, which was frequently evident even during the times when she felt unwell.

"She was a loving and generous child who spent much of the last few weeks of her illness making gifts to sell at her school Christmas fair to raise money for the hospital.

"She will be sadly missed."

Fund manager

Mrs Horlick hit the headlines last year when she was suspended by Morgan Grenfell for alleged disloyalty.

She flew to the company's headquarters in Germany, followed by newspaper photographers, as part of her campaign to get her job back.

In January, she launched the UK arm of Societe Generale Asset Management (SGAM), which invests large sums for institutions such as pension funds.

She has also campaigned for the Leukaemia Research Fund and last year dedicated the proceeds of her book, Can You Have It All?, to Great Ormond Street Hospital