Dressed in a white outfit delicately striped with gold and carrying a white tambourine, one of the contenders in Nigeria’s presidential election steps out of a white Rolls-Royce and strides up the aisle of the Household of God, flanked by bodyguards.

Chris Okotie, a 1980s pop star turned pentecostal pastor and four-time presidential candidate, is leading the service in the church he founded 32 years ago. For close to five hours his glamorous congregation is kept rapt with a medley of his greatest gospel hits, interspersed with prayer, speaking in tongues and a sesquipedalian sermon on the five foolish virgins. Young women in sweeping sparkly dresses sing along adoringly as ageing Nollywood stars boogie at the back.

Chris Okotie photographed in church on Sunday. Photograph: Andrew Esiebo/The Guardian

In 2003 Okotie became the first pentecostal pastor to run for president of Nigeria, which heads to the polls on Saturday. Since then the pentecostal churches – which place a special emphasis on a direct personal experience of God – have continued their exponential growth across the country and continent. Pentecostals make up 35% of all Christians in Africa, according to the World Christian Database, up from 13% in 1970. In Nigeria, their leaders have come to wield major political power.

This year, the two presidential frontrunners are both Muslim – the incumbent, Muhammadu Buhari, and the former vice-president Atiku Abubakar.

But the “pentecostalisation” of politics, which began 20 years ago, is continuing unabated, experts say, and the democratic process is shaped by powerful pastors, who regularly weigh in on elections. Some pastors even tell their flocks which way to vote. With no pope or archbishops to tell them what to do or say, and therefore no limit to their political activities, pastors have grown in their ambitions.

Though the highest Okotie has ever finished is eighth, he still considers himself and his Fresh party to be the solution to Nigeria’s problems. He has offered himself to the two leading candidates as a president everyone can agree on – what he calls a “consensus remedial facilitator” – in an interim government, though the chance they will go for it is slimmer than a communion wafer.

Chris Okotie departs from the service he held at his church in Ikeja, Lagos, on Sunday. Photograph: Andrew Esiebo/The Guardian

Traditionally, the highest office of the vast west African country has alternated between Muslims and Christians. Though northern Muslims have had only a slight advantage, being in office for about 33 of the 58 years since independence, most Nigerians think they have dominated, and Nigeria’s pentecostals are increasingly competing with them for state power.

Many Nigerian Christians fear the “Islamisation” of their country, pointing to the rise of Boko Haram in the north-east over the past decade, the spread of Sharia law across many northern states in the early 2000s, and attacks by mostly Muslim herders, who are often unfairly perceived as waging a jihadist campaign against Christian farmers. At least three priests have been killed in as many years in the pastoralist crisis in the Middle Belt, and the perceived nonchalance of the presidency about the issue has turned many Christians against the government.

Going into this Saturday’s election, many Christian Nigerians see Atiku, as Abubakar is popularly known, as more liberal than Buhari – and therefore more friendly to them, and more likely to deal with these threats.

Buhari, however, has on his side Yemi Osinbajo, the vice-president and a pastor from the Redeemed Christian Church of God, which has over 20,000 branches in 198 countries as well as its millions of Nigerian adherents.

A campaign poster in Abuja for Muhammadu Buhari and his vice-president, Yemi Osinbajo. Photograph: Ben Curtis/AP

In picking Osinbajo, Buhari was continuing to recognise the major political clout of pentecostal Christianity in his country, which is home to some of the world’s biggest megachurches. In 2011 he chose the influential Tunde Bakare of the Latter Rain Assembly, who gives his sermons titles like The Technology of Wealth Transfer and The Termites of Destiny.

Osinbajo and his faithful flock may have been a deciding factor in their 2015 victory, despite the fact that David Oyedepo, the founder of Winners’ Chapel, who preaches a prosperity gospel and has described himself as “dangerously wealthy”, told his congregation to pray for his opponent, the incumbent Goodluck Jonathan, to win.

Quick Guide 2019 Nigerian elections Show On Sunday 16 February, 84m voters will choose who leads Africa’s largest democracy. Despite over 60 candidates, it is likely to be a choice between President Muhammadu Buhari, and former vice president Atiku Abubakar. President Muhammadu Buhari (APC candidate) Buhari's 2015 victory with his All Progressives Congress (APC) party was built on three promises: to rid Nigeria of endemic corruption, fix the economy and tackle security threats. The government says it is making progress in the fight against Boko Haram, but it is now in its tenth year, and the economy entered and climbed out of recession under Buhari. Opponents say his government is failing to tackle corruption, while Amnesty International say the army has been responsible for human rights abuses. After spending five months in Britain in 2017 receiving treatment for an undisclosed ailment, opposition groups said he was unfit for office, but Buhari, 76, says he is strong enough to serve. Atiku Abubakar (PDP candidate) Main opposition People's Democratic Party (PDP) candidate Atiku, 72, has been caught up in corruption allegations since serving as vice president from 1999-2007. He has repeatedly denied any wrongdoing. He has promised business-friendly policies to double the economy to $900bn by 2025. He wants to privatise parts of the state oil company, and create a $25bn fund to support private sector investment. Atiku's opponents have claimed he would exploit those pro-business policies to enrich himself and those around him. A divided country Nigeria is deeply divided between the mainly Muslim north and largely Christian south. There are more than 200 distinct ethnic groups. This has led to an unofficial power-sharing agreement, with the presidency alternating between north and south every eight years. It isn't just religion or ethnicity causing fractures. Half of Nigeria’s registered voters are aged 18-35. Many say their ageing leaders are out of touch, and supported a "Not Too Young to Run" campaign to encourage younger people seeking office. Election concerns 2015 was the only time Nigeria had a peaceful power handover since civilian government took over in 1999. Even then there was evidence of vote buying, voter intimidation, and other forms of corruption. International observers fear election interference and rigging this time around. Last month, Buhari triggered a constitutional row when he suspended the chief judge, who has a crucial say in resolving election result disputes. Path to victory The candidate with the most votes is declared winner, as long as they have at least one-quarter of the vote in two-thirds of Nigeria's 36 states and the capital. Otherwise there is a run-off. Martin Belam and agencies Photograph: John MacDougall/AFP

Ebenezer Obadare, professor and author of the new book Pentecostal Republic, said that the “old story” of the interaction between religion and democracy had changed with the rise of the pentecostal churches.

“What the church wanted [in the past] was to be on an equal footing with Islam. Now, Christians do not just want to stand on an equal footing – they want power themselves,” he said.

Pentecostal churches are forcing Muslim leaders to up their game to keep their hold on power, Obadare said. God is invoked on everyone’s side.

The pentecostal church has been growing as part of a wave of religious fervour rising in Nigeria since the early 1990s. As the standard of living fell through both military and civilian administrations, citizens clung to their faith for salvation and respite. Pentecostals multiplied in the south, giving purpose and the promise of miracles to their converts.

Okotie leads the ‘praise and worship’ session of his Sunday service. Photograph: Andrew Esiebo/The Guardian

Whoever is in power, working together – what Obadare calls an “inter-religious political bromance” – is crucial. In the 2015 presidential election, Jonathan’s national security adviser spent billions of naira employing marabouts – Muslim holy men – from Saudi Arabia and north Africa to pray for his re-election, according to Nigerian media. Marabouts have enjoyed special access to the presidency since the 1980s.

In an interview in his marble antechamber after the service, Okotie delivers his analysis in the same style as his sermons.

“The things that divide us are ethnicity and religion, so we must rise above the pastiches of religion, the mosaic of ethnicity and whatever it is that separates us to an altitude where these cleavages diminish into mere superficial lacerations in the terrain of national integration and that’s the message that I’ve been given and that we can translate the paraphernalia of our diversity into the apparatus of national unity because we have an aboriginal connectivity that cannot be vitiated by politics, religion or ethnicity and we need to realise that and if we can embrace this philosophy then there’s hope,” he says, hardly pausing for breath. That was to say, an increasingly divided Nigeria should forget their differences and come together under him.

“The Chris Okotie option is the only viable option,” the author of Nigerian classics Show Me Your Backside and Yes I Know He Lives adds, his aides standing reverentially around.

Jesus, he says, will be a political leader in his second coming. “What we’re doing now is going to be a microcosm of what is going to come.”