Sambrook received the award at a ceremony held at the London headquarters of the British Academy of Film and Television Arts this evening.
The award, which was set up by Private Eye and the Guardian in memory of campaigning journalist Paul Foot, who died in 2004, recognises the year's best investigative journalism.
Announcing the winner, Private Eye editor Ian Hislop said Paul Foot would have been impressed by the standard of entries, which he said showed that "investigative journalism is very much alive."
Sambrook was awarded the accolade, and £5,000 prize money, in recognition of her work, which has been reported in a number of publications including the Guardian, the Independent and Private Eye.
Eamonn McCann, who was shortlisted for his reports on the British army's actions on Bloody Sunday, was given a Special Lifetime Campaign award of £2,000 for 40 years of campaigning journalism.
A prize of £1,000 was awarded to each runner up from the shortlist, as shown below:
- Jonathan Calvert and Clare Newell (Sunday Times) - on MPs and peers seeking cash for influence
- David Cohen (Evening Standard) - on the plight of the poor in London
- Nick Davies (Guardian) - on phone-hacking conducted by the News of the World
- Linda Geddes (New Scientist) - on evidence that DNA tests are not always accurately interpreted