Hamdeen Sabbahy has the photographs of two men in a frame on his desk: his father, with the lined, sun-worn face of a peasant farmer, and Gamal Abdel Nasser, widely described as the first leader of an Arab nation to challenge Western dominance of the Middle East.

Their inspiration has carried him through five decades as an opposition activist, and has now pitched him headlong into a race for Egypt's presidency. When Egyptians go to the polls this month they are widely expected to return a landslide victory for Abdel Fattah al-Sisi, the former military chief with austere personal habits and an austere vision for Egypt – hard work, sacrifice, and certainly no more protesting.

His lone challenger is Mr Sabbahy, an avuncular and warm lifelong oppositionist with roots among the impoverished farmers of the Nile Delta who promises to fulfil the aspirations of the revolution that broke out three years ago: bread, freedom and social justice.

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In a region dominated by kings, Islamists and military strongmen, Mr Sabbahy claims to offer something different. "If we manage to reach power we will create a model that is an example, not just for Egypt, but for the whole Arab region," he tells The Independent on Sunday.

The two candidates have very different visions. Mr Sisi backs a law introduced last year that makes protesting illegal without police permission; Mr Sabbahy promises to repeal it and release the "unjustly imprisoned", including leading lights of Egypt's revolutionary youth movement.

In the wake of televised interviews with the two candidates last week, Mr Sabbahy's social democratic vision of helping the poor seems to be gathering momentum. For the revolutionary youth, Mr Sabbahy is not an ideal candidate ﻿but, on social media and in downtown Cairo cafés, the mood seems to be turning from a boycott to grudging support.

On television and on the streets, he seems comfortable and at ease, compared to Mr Sisi, who appeared overbearing and awkward in the recent interviews. Mr Sabbahy says Egypt's problem is that, despite superficial changes, the same people have stayed in power and "Mubarak loyalists" have remained in Mr Sisi's campaign.

Growing up, Mr Sabbahy was acutely aware of the daily struggles of his poor village, on the shore of a lake, which he fished as a young man. When Mr Nasser brought British rule to an end in 1952, his rhetoric of justice and equality coursed through the Delta. Mr Sabbahy remembers how it inspired him. "I am a son of that time," he said. In primary school, he would give speeches and once led a student strike after the principal beat a pupil. At university, he publicly challenged President Anwar Sadat during a televised debate, a taboo at the time.

After graduation he founded a series of political parties. He says that his generation of activists developed a "street Nasserism" which recognised faults in Nasser's state, and incorporated support for democracy and human rights. Mr Nasser's successors did not share those views and, for his activism, Mr Sabbahy was arrested 17 times, imprisoned eight and tortured once.

One of the prisons in which he was detained, the Citadel in Cairo, was subsequently decommissioned and converted into a tourist attraction. Mr Sabbahy took his children to see the cell in which he was held in solitary confinement. Like many other political prisoners, the experience only hardened his convictions.

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"If it hadn't been for prison, I would not have been able to read the terrible translation of Edward Said's Orientalism that I had with me," he says.

In 1995, he stood in parliamentary elections as a candidate for his home district. He finally got into parliament in 2000.

In Egypt's first post-revolution presidential election, Mr Sabbahy surprised observers by coming a strong third in the first round with 21 per cent of the vote.

From the point of view of the Muslim Brotherhood, Mr Sabbahy is just another backer of the July coup which forced them from power. Although he opposed the military taking power, he backed demonstrations against the Brotherhood, and a protest four weeks later to "authorise" Mr Sisi to deal with "terrorism", which meant the Brotherhood.

Mr Sabbahy also maintains that the police clearance of two Brotherhood Cairo sit-ins in August was necessary, although they left around 800 people dead. He says the operation violated human rights standards. For young Brotherhood activists who have lost friends to police bullets, that isn't good enough.

Others question whether his populist and sometimes vague policies are feasible for an economy in crisis. He argues that only fighting corruption and elite interests can revitalise Egypt for both workers and the private sector.

It is the financial backing of Saudi Arabia, Bahrain and Kuwait that is keeping Egypt afloat. "In truth, they have paid money so that we continue the war against the Brotherhood," he acknowledges. But Mr Sabbahy does not believe their influence would curtail his leftist programme because he, too, would see that the Brotherhood did not return.

Hamdeen Sabbahy is chiefly remarkable because he has chosen to participate despite the overwhelming weight of the state institutions and private wealth behind Mr Sisi's bid for the presidency. Other prospective candidates all withdrew from the race in quick succession, some saying there was no prospect of a genuinely free and fair election.

Mr Sabbahy's critics say that his candidature legitimises an illegitimate process. But, in his bustling campaign offices full of young activists last week, there was a sense of hopefulness rare in Egypt today. "It's good to be working on something positive," one of them, Karima Aboul Nour, said.