“Hummah, hummah, hummah,” sings speech and drama therapist Rebecca Thompson. “Hummah, hummah, hummah,” her class sings dutifully in reply. “Sit up nicely! Humming is a great way of warming up your voice,” she enthuses. “Release that sound… Open up the resonators! Do you get a sense of your voice opening up?”

It is a bleak Monday afternoon and a miasma of sullen suspicion hangs in the air of the chilly converted orangery where Thompson’s voice workshop is taking place. Her class is a group of trainee vicars at Trinity College, Bristol. I get the impression they are worried about losing their dignity or looking “silly”, like a bunch of leaden party guests forced to participate in a jolly game of charades against their will.

“Diction is a bit of a dirty word, isn’t it?” Thompson continues chummily. “But lapsed diction will inhibit the travelling power of your voice. Now we’re going to do some tongue-tip hard consonants.”

Phonetically, she says the letters T, D and L: “Tuh. Duh. Luh. Tuh Duh Luh. Isn’t it lovely to feel that tongue tip having to work really hard?” Her students don’t look overly thrilled about it. “Tudulluh, tudulluh, tudulluh,” they chant back with a dreary obedience.

This type of training in voice and presentation skills is now commonplace in theological colleges throughout the UK. Modern-day clergy are expected to master modern communication techniques. Just as politicians and businessmen receive media training and learn how to “exude” and present themselves to best advantage, so must the new generation of vicars. Alongside Christian Doctrine and Practical Apologetics, they also learn how to work a crowd and develop some showbiz-style presence in the pulpit. (“C’mon! Eyes ’n’ teeth, Vicar!”) The days of the simple country clergyman droning his way through a tedious sermon before his uncomplaining flock have all but disappeared.

“I think churches and congregations used to be more long-suffering, but expectations have now changed,” says the Rev Rod Symmons, Trinity College’s homiletics tutor. “We have so many messages coming at us in so many different ways that unless vicars can communicate effectively, people just don’t have the emotional energy to listen.”

“Modern technology has made communication more intimate,” suggests the Rev Chris Green, vice principal of Oak Hill Theological College in London. “You no longer have to raise your voice to speak to 2,000 people. You can speak in quite a normal, living-room sort of voice and be heard all around the building with microphones and so forth. Many churches now have cameras and screens around the place, and that also increases the intimacy, because even if you are sitting at the back you can still see the speaker’s face quite clearly.”

Being seen in glorious Technicolor and the increasing availability of sermons on DVD or by podcast have raised the bar considerably. Theological colleges are taking advantage of this same technology for training purposes. Students are filmed preaching, with their sermons played back to them to illustrate where their technique can be improved. Footage of famous preachers and different sermon styles is studied in depth. Students at Oak Hill are coached in voice and presentation skills by a RADA-trained actor, once with the Royal Shakespeare Company.

Trinity College students are allocated to weekly preaching teams and take it in turns to speak at local churches and receive constructive criticism from their peers. This Sunday it is the turn of second-year student Olly Mears, aged 27.

We’ve all seen those old-fashioned cartoons showing a doleful missionary being boiled alive in a large pot by cannibals – I can imagine Mears in just such a situation. His face shines with eagerness and even his hair curls with a muscular Christianity. He is enormously likeable – gentle and funny and still possessing the awkward “gruntiness” of the typical teenager.

Redland Parish Church is in the posh part of Bristol. The congregation has an air of well-dressed prosperity – hair is crisply permed and one chap even appears to have ironed his knitwear. The members of Mears’s preaching group are lurking in the pews, pencils sharpened, ready to take notes on his performance. Sermon Criticism Forms (popularly known as “sermon crits”) are distributed among them and given to regular members of the congregation. Mears looks increasingly nervous. He has spent Thursday afternoon and most of Friday composing his sermon in Starbucks. Eventually, his big moment arrives.

“Today is a day of hope,” he begins, a mild sheen glistening on his upper lip. Mears’s sermon is based on the three Bible readings for the day (Isaiah ii, 1-5, Romans xiii, 11-14, and Matthew xxiv, 36-44). His themes are awakenings, hope, fear, vulnerability and the transition from darkness into light. It is a complicated weaving job that takes in monsters in the dark, birth, trade justice, consumerism, the death toll in Iraq, and more. The highlight is a personal anecdote about climbing a mountain in the dark to witness the sun rise.