Premadasa is the son of R. Premadasa, the president who was assassinated by the Tamil Tigers in 1993.

For his part, Gotabhaya denies having been the architect of “white van abductions”, in which some

journalists and suspected Tamil separatist operatives disappeared, never to be found again.

His supporters have ridiculed Premadasa as “pad man” for his appeal to women voters with promises to improve menstrual hygiene.

Still, there have been suggestions that Premadasa is narrowing the gap, fuelling predictions that an upset could be on the cards.

A significant amount of votes are likely to be cast along ethnic lines. Rajapaksa should win a large percentage of the Sinhala majority vote while Premadasa can expect strong support from minority ethnicities. But this might not be enough for Rajapaksa, who will be mindful that in 2015 his brother Mahinda lost his third bid for the presidency when the Sinhala community did not vote for him in the expected numbers.

WHAT DO THEY STAND FOR?

The incumbent UNP surged to power in 2015 on a platform of tackling corruption and promoting democracy and good governance, but is widely seen as having failed to deliver. Indeed, the party itself has largely abandoned its “good governance” platform in favour of a more populist message of representing the poor and “uplifting the economy”.

Premadasa, the UNP’s candidate, has made this the signature rallying call of his campaign, reminding voters of the pro-poor initiatives and poverty alleviation programmes for which his father was known.

He has said he is committed to women’s rights and has vowed to “wear the ‘padman’ label proudly” in a conservative Buddhist society where menstruation remains a taboo subject.

In contrast, Rajapaksa’s platform prioritises national security and a “modern, functional economy” – something he says the governing party has been unable to achieve.

He, too, is capitalising on the past, in his case memories of his performance as defence secretary in the government of his brother Mahinda and his reputation for prosecuting the war with ruthless efficiency, something widely acknowledged by friend and foe alike.

WHAT’S AT STAKE?

That depends on whom you ask. Some see the election as a referendum on the future of the UNP, which despite its anti-corruption message presided over a scandal at the Central Bank involving alleged insider dealing of bonds that cost the exchequer several billions of rupees and is referred to by many locals as the biggest heist in the country’s history.

Others are more worried about Rajapaksa’s background and reputation as a ruthless military man. Rajapaksa has himself brushed aside questions about war crimes during the final offensive of the Tamil war during which some 40,000 Tamil civilians are said to have been killed. Sri Lankan

governments including the former Rajapaksa regime have contested these numbers, which

have also been refuted by personalities such as Lord Naseby of the British House of Lords who, citing WikiLeaks, claimed the number could be as low as 7,000.

“Why are you talking all the time on the past? Ask about the future,” Rajapaksa said recently. “I am trying to become the president of the future Sri Lanka. So if you concentrate on the future, it is better.”

There are other doubts over Rajapaksa, too. He is out on bail facing prosecution for allegedly siphoning off hundreds of thousands of rupees of state cash to build a monument for his parents when his brother was president.

Rajapaksa has denied allegations that he received millions of dollars by way of kickbacks from a second-hand aircraft purchase from Ukraine in 2007. He has not been indicted but police are investigating the purchase.

He also faces a civil suit in the United States for allegedly ordering the torture of a Tamil man and several others when he was in power.

Another civil action against him in a US court was rejected on the basis that Rajapaksa had “foreign official immunity” for allegedly causing the death of an anti-establishment newspaper editor in Sri Lanka in 2009.

His opponent Premadasa, meanwhile, has been summoned by the Presidential Commission of Inquiry on Corruption over alleged corrupt practices in granting a large number of irregular appointments to political supporters. Police are investigating.

WHO ARE THE VOTERS?

A majority – about 75 per cent – of the 15.9 million people registered to vote in this election are Buddhists belonging to the Sinhala community. The rest are either Tamil Hindus or Muslims and the bulk of these groups live in the formerly war-torn northern and eastern provinces.

Just over 30 per cent of registered voters are classified as “youth” – under 30 years old – and 1.55 per cent are first-time voters.

There is no electronic polling and all ballots will be cast on paper.

The significance of the youth vote has led to speculation that social media could influence the result. The Elections Commissioner has conceded he has no control over social media, even though traditional media is required to give equal coverage to all candidates. However, he has also admitted – rather sheepishly – that his “guidelines” are being breached by traditional media, too.

WHAT’S IT TO DO WITH CHINA, INDIA, U.S.?

“China is not an issue in this election but the US’ role has come under scrutiny because of the current government’s move to sign the Millennium Challenge Corporation compact,” said Shamindra Ferdinando, a political columnist.

The compact, according to opposition parties, cedes large swathes of land to almost absolute US control, a claim the government denies.

Rajapaksa has vociferously rejected the compact but is accused in turn of being in thrall to Chinese influence. Indeed, after his brother’s defeat in 2015 the Rajapaksas were widely criticised for leading Sri Lanka into a Chinese debt trap.

Ironically, since the UNP administration handed over the strategically important Hambantota Port to a Chinese company on a 99-year lease amid struggles to repay the government’s debts with Beijing, the same criticism could prove costly at the polls for Premadasa’s party.