Park Won-soon, a civic rights activist running as an independent candidate for Seoul mayor, started a web site this week to raise Won4bn ($3.4m) for campaigning. The site crashed temporarily on Tuesday, unable to cope with the flood of donations.

Despite this technical blip, Mr Park, a leftwinger who is leading polls before the mayoral vote on October 26, hit his fundraising target in only three days, mainly through small payments.

Mr Park’s popularity suggests South Korean voters are swinging to the left before next year’s presidential elections as ruling conservative politicians struggle to counter the left’s promises to expand welfare spending in Asia’s fourth-biggest economy, which runs at only a third of levels in large European states.

The surprising strength of an independent also reflects disenchantment with South Korea’s polarised two-party system and its inability to tackle corruption and growing social inequality. It would be extremely unusual for an independent to reach a position as prominent as mayor of Seoul, representing almost a quarter of the country’s population.

Mr Park rose to prominence as a lawyer opposed to the military dictatorship that fell in the late 1980s. He has founded a network of second-hand stores called Beautiful Shops, intended to help the poor.

His poll ratings rose sharply after another independent politician, Ahn Chul-soo, withdrew his candidacy for mayor to support him. Mr Ahn, the founder of a top software business, is a critic of the country’s policy of favouring industrial conglomerates – chaebol such as Samsung and LG – which he describes as zoos where employees are the caged animals.

“Mr Park and Mr Ahn look like enterprising, spirited men. The most important thing is they are so different from our regular politicians,” said Lee Ho-won, an employee at an engineering company.

Despite swelling popular support, Mr Park faces severe challenges.

“Korea’s politics are unlikely to change with the emergence of one or two crusaders because existing practices are so entrenched and vested interests are so strong,” said Shin Yul, professor of politics at Myongji university. Korea is often criticised for its “old boy” network of chaebol, bankers and civil servants who resist reform.

“The independents have somehow come to represent the people’s desire for new values rather than being great themselves …I am sceptical they can be effective politicians.”

Conservative politicians and newspapers have also attacked Mr Park for being a champagne socialist, who lives in an upmarket district while dressing down to win popular favour.

Mr Park must now survive a primary vote against a candidate from the Democratic party, the main leftwing party, to be selected as the official unity candidate. The DP’s candidate, Park Young-seon, a former television anchorwoman, trails Mr Park in polls but the process of selecting a unity candidate, which begins next week, is complex. It involves a television debate, two opinion polls and a vote among a 30,000-strong electoral college.

The selected leftwinger will then face Na Kyung-won, from the ruling conservative Grand National party. As a former judge, she epitomises the establishment but her support of the disabled – like her own daughter – wins her broad public sympathy.

She concedes Korea needs to spend more on welfare – particularly in terms of child benefit – but is arguing that a European-style safety net is unaffordable. Mr Park says such welfare must become a basic right.

A more glamorous campaigner than Mr Park, Mrs Na has been splashed across newspapers serving chickens in a market and posing with Hyun Bin, a popular actor.

Polls show she is narrowing Mr Park’s lead and has about 43 per cent support compared with his 49 per cent.

Additional reporting by Kang Buseong

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