H ELD WITHIN the blackened walls of a disused department store, the evening service at Portsmouth’s Harbour Church resembles a gig in a trendy nightclub. Guitars take the place of a church organ; hymn books have been swapped for plasma screens displaying song lyrics. Alex Wood, the vicar, favours skinny black jeans rather than a clerical robe. Swathed in blue light, his congregation of teenagers and 20-somethings sing their way through a playlist of uplifting Christian rock.

Churchgoing has plummeted in Britain. Only 740,000 worshippers regularly make it to Anglican churches on Sundays, half as many as in 1970. To halt this decline, the Church of England has launched an evangelism drive. Part of its strategy is to attract young agnostics by “planting” churches, an American model where members of a healthy church set up a new one elsewhere. Holy Trinity Brompton (HTB), a thriving evangelical church in west London, has been planting churches since the 1980s. Now the clergy’s top brass want to emulate its success. According to Ric Thorpe, the Bishop of Islington and a former HTB man, 2,400 church plants are planned by 2030.

New evangelical churches have proved capable of astonishing growth. Harbour Church was planted by 15 missionaries from St Peter’s in Brighton in 2016. Now its four services pull in around 600 worshippers each Sunday. St Peter’s itself was set up by 30 HTB parishioners in 2009 and now boasts a flock of 1,000.

Their success lies in repackaging Christianity to appeal to the young, says Bishop Thorpe. Harbour Church’s main morning service (where worshippers have an average age of 27) starts with pastries and micro-brewed Brazilian coffee; the evening service (average age: 19) is followed by hot dogs and craft beer. Ryan Forey, a trainee priest at the church, is frustrated by perceptions of Christianity as stuffy. “Jesus’s first miracle was turning water into wine; he kept the party going,” he says.

Harbour Church says it is not a church for people who are already Christian. Yet some worry that these young, vibrant churches are not winning new converts as intended, but rather cannibalising existing congregations. In 2016 a study of five HTB churches in London found that 38% of parishioners had transferred from another church. A show of hands at Harbour Church suggests that about a third left another congregation to join. Another large group are students looking for a term-time church. One worshipper explains that he defected from his old church because it was rigid and traditional. Mr Wood says he does his best to persuade such parishioners to return, but if they claim God called them to his church there is little he can do.

Planting is changing the face of the Church of England. Not so long ago, evangelicals armed with guitars were politely dismissed as an oddball fringe. But Justin Welby (who attended HTB before he was ordained) has staked his career as Archbishop of Canterbury on getting more bums on pews. The missionary zeal of evangelicals and their eagerness to plant churches means they are at the forefront of his push.

This rankles with some vicars. Talk of a takeover is rife. Alarm bells ring when HTB comes to town with a new plant, as priests fear losing the youngsters in their flocks. Rural parishes complain that funding goes to flashy urban ventures. And despite the guitars and coffee, evangelicals tend to be “anti-gay and a bit funny on women”, says Linda Woodhead, a sociologist at Lancaster University. She warns that, as the church grows more evangelical, it risks morphing into a sect that appeals to a dwindling pool of conservative enthusiasts.