Five years ago, while Alex McLean was on his gap year volunteering at a hospice in Uganda, he arranged to visit the country's Luzira maximum security prison. He was so shocked by what he saw that it changed his life.
The prison was built for 600, but held 3,000. Its death row was built for 60 and held 320, and teenagers convicted of petty crimes were facing the firing squad. Conditions were harsh and inhumane in the prison, but they were worse in the prison hospital.
"The place stank," says McLean. "People were handcuffed to beds, and some had maggots crawling over them because they couldn't help soiling themselves and ended up with maggots feeding on them.
"One man was lying on the floor with incredible bedsores, waiting to die. We had to tie bandages round our noses because his flesh was rotting."
Determined to do something about it, McLean founded the African Prisons Project. He showed photographs of the conditions at Luzira to people at home and quickly raised £3,500 to return and refurbish the hospital and supply it with books.
In 2006, the charity also improved conditions at a detention centre in Sierra Leone, where children had been sleeping on a cold floor with one blanket between three. The centre now has beds, pillows and mattresses, and an agricultural project helps the children grow their own food.
These achievements won McLean the Beacon Prize for Young Philanthropist of 2007 and the prestigious main prize of £30,000 in the annual Beacon Fellowship awards, which recognise people who have made exceptional contributions to charities or organisations that benefit the public.
Other plaudits have included a song by a choir of condemned men at one Ugandan prison, which described him as a "God-sent messenger of hope".
McLean, now 22, combines his charity work with studying for a masters degree in law. He is interested in human rights and its application to criminal justice and the death penalty, and hopes one day to be a judge.
On the day of this interview, he has just returned from Uganda. Later he is due to volunteer as a nurse at Trinity Hospice in south London, which he has been doing since he was 16. The next day, he has a placement at a magistrates' court as part of his course. He is also planning to refurbish another 200-bed prison hospital in Uganda. His next project is in Zambia, which has the most overcrowded prisons in Africa.
"I want to have a model for other African countries so that, with a relatively small amount of money, we can make massive changes to medical and educational facilities," says McLean.
The amounts McLean has raised have increased, and so has the scope of his work. The African Prisons Project's costs are low because McLean has developed an infrastructure that relies on local people. "The project empowers them to make their own changes," he says.
He puts his success down to making simple improvements. Prisoners, many of whom are tradesmen, renovate the prison, saving labour costs and boosting morale.
The project asks companies in the UK to donate books and medical equipment, and asks businesses local to the prisons to help with donations of linen and paint. This spreads awareness about prison conditions and keeps costs down.
"The needs of prisoners are unique," says McLean. "Wherever we work, we bring local people in to see for themselves and encourage the media to cover things on the radio or TV.
"Rather than just sending money out to prisons to make them better, you need to change the mentality. Charity doesn't have to be flash."
2008: Studying for masters degree in law, Nottingham University
2007: Completed law degree, Nottingham University
2004: Founder and director, African Prisons Project
2003: Gap year in Uganda
2001: Volunteer nurse, Trinity Hospice, London
1996: Student, Kingston Grammar School, Surrey