(CNN) -- Mahmoud Sarsak is twice the man he used to be.
The diminutive Palestinian soccer player is sitting in a small cafe in central London, tired but otherwise surprisingly healthy for a man who had lost half his body weight during a hunger strike 12 months ago.
It is his first visit to the British capital but, like many who try to leave Gaza, his journey was long and far from easy.
"The Rafah border (between Gaza and Egypt) was closed for days because of the kidnapping of soldiers in Egypt. It was hectic," explains Sarsak, a talented striker who had once been called up to the Palestinian national team squad.
"I managed to cross the border by miracle. I was the last one to be allowed to cross."
But Sarsak says he wasn't in London to pursue his dream as a professional soccer player, or to spend time there as a tourist. He was there to protest outside the UEFA Congress, held recently in the UK capital, to campaign for a boycott of the European Under-21 Championship which started in Israel on Wednesday.
"How did UEFA give this to Israel?" he says, shaking his head. "Why did they think it was acceptable despite knowing the violations of human rights the Israeli state conduct on a daily basis?"
Sarsak claims he has experienced this first hand. In fact, he says he is lucky to be alive.
This time last year he was on the verge of death, he says. The 23-year-old says he had lost half of his body weight in a three-month hunger strike after being held without charge in administrative detention by Israeli authorities for three years.
Under administrative detention, a person can be held indefinitely without charge or trial on secret evidence.
The Israelis have accused Sarsak of having links with the extremist organization Islamic Jihad and of being involved in terrorist activities. A senior Israeli security source with knowledge of his case, speaking on condition of anonymity, told CNN: "The individual in question was held in administrative detention due to security-related matters, including involvement in attacks on Israeli forces, and planned to perpetrate suicide bombings." But Israeli officials offered no specific response to questions about why Sarsak was released.
He was let free last July, emaciated and pale, after the likes of FIFA president Sepp Blatter intervened on his behalf, appealing to the Israel Football Association for help.
For much of the past year, campaign groups and famous names in soccer, including former Mali international Frederic Kanoute, have called for a boycott of the U21 tournament due to Israel's treatment of Palestinians, including athletes like Sarsak.
A petition was raised by the pro-Palestinian campaign group Red Card Israeli Racism, attracting more than 8,000 signatures. An open letter was also sent to British newspaper The Guardian in May, signed by Archbishop Desmond Tutu as well as a raft of other politicians and celebrities.
"UEFA is rewarding Israel's cruel and lawless behavior by granting it the honor of hosting the European Under-21 finals next month," the letter read.
"UEFA should not allow Israel to use a prestigious football occasion to whitewash its racist denial of Palestinian rights and its illegal occupation of Palestinian land."
But, for some of those campaigning for a boycott of the tournament, they say the most damning evidence comes from Sarsak's own experiences while in detention.
"This (hunger strike) was the only way left to achieve my liberation," he claims. "The Israelis killed my hope, killed my dreams, killed everything. It was either to live in dignity or be buried underground."
Sarsak grew up in Rafah, a Palestinian city in southern Gaza, with little other than soccer.
"It runs through the family blood. All of my brothers played," he says.
"When I was growing up I looked up to Palestinian players. We didn't have TV so we didn't know anything of any international players. We looked up to them because they were so confident and happy. They made people smile. They brought spirit and life into the destructive places we were living in. That's what I wanted to do. Put smiles onto people's faces in such a hard place to live."
It soon became clear that Sarsak had talent. At 14 he became the youngest player to represent the Rafah soccer team, and was called up for an international tournament in Norway. Soon he came to the attention of the Palestinian national team, which has been recognized by FIFA, soccer's global governing body, for more than 15 years.
But it wasn't until 2009 that Sarsak was offered a professional contract with a team in the West Bank. Finally he managed to secure the hard-to-come-by permit required by Palestinians to leave Gaza.
"I was delighted," Sarsak recalls of the day he left his home.
"Through football I would be able to help my family survive. I was on my way to establishing myself as an independent person. Building a home, building a family. The day before I traveled, all my friends came and celebrated. Everyone was delighted."
That dream turned sour. When he arrived at the Erez Crossing into Israel the situation quickly deteriorated, he said.
"A woman soldier and officer said I should go for an investigation. I wasn't worried as lots of people were being investigated," he said.
"I was surprised when my hands and legs were chained immediately. No-one else was. I thought, 'OK, something is happening.' "
It was the start of a three-year nightmare for Sarsak.
"They searched me and then put big black glasses on my eyes so I couldn't see. They took me with my chained arms and legs down into what felt like a big bunker underground. When I got there and took the glasses off I was sitting on a chair in front of an interrogator.
"I was harassed, brutalized, hit on the head with the guns they were using. They took me off into an army center where they called my brother and told him I was in prison. I spent 45 days there. I saw death many times throughout that period."
Sarsak claims that during this period he was physically and psychologically tortured.
"A human being is being kept in a place not suitable for an animal. It is a two-meter-by-two-meter bunker," he recalls.
"Damp. No sun. No air. It is not a place where even animals should be. At first I had 18 days of investigation. I was chained to a chair. My eyes were closed. I was not allowed to sleep for 18 days. I was beaten up, humiliated. I was put in a fridge for a time where I was frozen almost to death and then straight from there to the hospital. Every time you go through these cycles you feel like you are going to die. And you could die at any moment under those conditions."
The Israeli authorities deny any allegation that Sarsak was tortured. "Any claims he was physically mistreated in any way are totally baseless," the senior security source said. They also believe that administrative detention is a vital, and legal, security tool.
"Administrative detention is legal under international law," Israeli government spokesman Mark Regev said when asked about the use of administrative detention and why Sarsak was not brought to trial.
"We prefer not to use it, we prefer open court but sometimes this proves impossible. If you have sensitive intelligence material, hard-line terrorist groups will immediately and violently eliminate our intelligence sources. We use this sparingly. Where a situation like this arises we need to protect our security sources.
"The process is not arbitrary. There are checks and balances in place. You cannot be held for a few days before being brought before a judge. They can appeal all the way to the Supreme Court. The Israeli judiciary is fiercely independent and has no issue ruling against the government."
Sarsak maintains his innocence.
"If I actually had links with terrorists, why was I never charged? Never brought to trial justly?" he says.
"I spent three years in prison with no accusation. If I did have links I should have been brought to court. But in reality they had nothing on me. This was a false charge under which they kept me in prison. I lost three years of my life."
Back in London, later in the day, Mahmoud Sarsak joined a small but vocal protest outside the Grosvenor House hotel where the UEFA congress was taking place. He personally delivered the petition calling for the boycott of the tournament.
"I have great respect for the Palestinians," UEFA president Michel Platini told CNN when asked about the protests.
"We have solidarity with Palestinian football ... we have sent money, letters to press for the release of players and to get visas (but) Israel has just as many rights as anyone else to host a tournament. This shouldn't affect a youth tournament."
For the Israelis, the European Under-21 Championship is arguably the most prestigious international sports tournament ever held in the country. It is particularly poignant given that Israel used to be part of the Asian Football Confederation, even qualifying for the 1970 World Cup finals, until a boycott by its Arab neighbors forced the Israeli Football Association into the wilderness.
It was eventually accepted as a permanent member of UEFA -- European football's governing body -- in the 1990s. Tens of millions of dollars have been spent on hosting the tournament. Two state-of-the-art stadiums have been built, and two more renovated.
"Four years of hard work by all involved are coming to fruition," Israel Football Association spokesperson Michal Grundland said.
"We hope viewers and tourists will see Israel for what it really is -- a vibrant country with a rich culture, an absolutely phenomenal place for young people and tourists to enjoy and have fun, peacefully -- and not what it is perceived to be from the way it is usually represented in the foreign media."
For many Israelis, talk of a boycott is counterproductive. They say soccer is one of the few areas in Israeli society where Arabs, who make up around 20% of the country's population, are well represented. Virtually every Israeli league side has Arab players, with the exception of Beitar Jerusalem -- one of Israel's best supported teams -- which has never had an Arab player on its team. Five Israeli Arabs have been called up to the Israel side for the tournament.
"(That is) a much higher percentage than in the general population," Grundland said. "Soccer in Israel is a uniting sport. Four of the five Arab Israelis in the squad will be part of the starting XI."
Yet, as the protesters chanted outside the Grosvenor House Hotel for the tournament to be stopped, others within Israel believe that boycotts harm the Palestinian cause. Only recently, distinguished British scientist Stephen Hawking controversially boycotted a major international conference in Israel over the treatment of the Palestinians, sparking a debate as to how effective such actions actually are.
"You call these groups calling for a boycott pro-Palestinian. They are not. They are nihilistic and anti-Israeli," said Regev.
"These groups calling for a boycott of football are the same groups who call for a boycott when the Israeli philharmonic orchestra plays overseas. They boycott Israelis. I challenge you to find one person calling for the boycott of this football tournament who isn't calling for other boycotts too. They demonize Israelis and harm the creation of a Palestinian state."
The two-week tournament, which began Wednesday with Israel drawing 2-2 against Norway, is expected to go ahead as planned. Sarsak will spend the next couple of weeks touring the UK, speaking at public meetings about his experiences and why he believes UEFA is wrong to allow Israel to host the tournament.
"Michel Platini came to Palestine and saw the real situation. He said that he will carry the Palestinian cause and would advocate against the oppression of the Palestinian people," Sarsak says.
"He has completely changed his mind. He has given Israel a present on a platter of gold by giving them the honor of hosting the tournament."
Sarsak has made a good physical recovery from his hunger strike. As the tournament kicks off, he says he is haunted by the memories of his detention, the time he has lost and the mental scars he still endures. But, one day, he hopes to play soccer again.
"I still want to pursue my dream," he says, "because the Israeli intention was to destroy my dream and stop me playing football."