Christian television keeps me up at night. That's partly because I sometimes find myself watching it in the small hours, often in a state of total disbelief. Mainly though, it's because on British TV, there are people and programmes being broadcast every night which present at best a skewed version of the Christian gospel, and at worst, an outright heretical rewrite of the faith.

I think most of us suspect this to be the case. We use shorthand when we talk about some of those high-numbered Sky TV channels, referring to things like 'televangelists' and 'dodgy preachers.' In doing so, we square them away as a quaint irrelevance; not really advancing the Kingdom of God, but not really doing much damage either. That's a response I've been guilty of in the past, and I think it's a cowardly one.

I'm clearly not the first of only person to have spotted this. David Robertson's excellent critique of GOD TV shone a light on the flawed ideology at work behind the most famous Christian TV channel borodcast in the UK. He highlights GOD TV's worrying focus on money and power, and warns Christians against buying into that kind of dangerous and off-piste theology. I think there's more to say though; I think that these channels have the potential to undermine and even skewer our attempts at evangelism.

We often think of the local church as the public 'face' of Christianity for those who don't subscribe to it. Weddings, funerals, the occasional festive service; these are the places where people encounter Christianity cold, and form their opinion on whether it's worth exploring. I'm sure that's true for many people, but for others, there's another first point of contact, and it's those Christian TV channels.

At last count, there are about 20 explicitly Christian channels on Sky. These include a handful which don't really fit the profile I'm concerned with – UCB, Revelation TV, the Catholic Television Network, and a couple which only seem to play music videos. I have no quarrel with these stations; at times they produce programming which could be very thought-provoking to the late-night channel hopper.

The cast of characters I've discovered on the remainder though is nothing short of extraordinary: disgraced televangelists and modern-day snake oil salesmen, crazy end-times prophets and incomprehensibly shouty pentecostals. There's an awful lot of talk about Israel; there's a fair amount about the coming apocalypse (those two subjects are often linked). And there's one subject which comes up over, and over, and over again. Money.

I can cope with difference of opinion over the place and importance of the Holy Land. I can even reconcile the entire TV series dedicated to 'End-Times-Watch'. The problem is the murky undercurrent which seems to bubble under the surface of so many of these channels; the promotion of the Christian faith as a route to financial prosperity, and a team of con-artists competing to sell you their version of the dream.

The con works like this: you sow a 'seed of faith' into the particular ministry which is broadcasting, and God will repay you with innumerable financial blessings. The 'seed' is a clever way of avoiding having to use the words 'cash' or 'money', but that's exactly what they want from you. Sometimes the seed is a specific, and entirely arbitrary amount ($58 is a popular figure); sometimes, if the presenter is feeling really ambitious, they'll ask for hundreds or even thousands. Often the sale is shrouded in a purchase; your donation rewarding you with a book of their collected writings or even songs, but there's little doubt that these are only the first steps on a lifelong journey of requests for further cash.

It's worth naming a few examples at this point, just so you don't think I'm creating a straw man. So there's Pastor Mike Murdock, Senior Pastor of The Wisdom Centre in Fort Worth, Texas, who mixes sales of his self-published books of 'wisdom' (that's Mike's thing) with on-screen requests for donors to 'sow an uncommon seed' into his ministry. In one programme, he reportedly asked for 70 people to give him a donation of $8,500, and of course, he always promises the viewer that this kind of generosity will be repaid by on outpouring from heaven like they've never known. He often brings on guests who, like happy testimonials at a timeshare presentation, will grinningly report how the process worked for them. More often than not, these people, men like Dr Todd Coontz (last seen pitching for donations at a post-Rory Alec God TV), also run fledgling prosperity 'ministries' of their own.

Or there's 'Evangelist' Jimmy Swaggart, the almost-octogenerian patriarch of Jimmy Swaggart Ministries who enjoyed huge popularity in the 1980s before his implication in two sex scandals. This led to his suspension and then defrocking by the Assemblies of God, but Swaggart soon returned with a non-denomiational ministry, now based in the Family Worship Center in Louisiana. Today, Swaggart and his son Donnie are prolific on Christian TV, appearing on several UK channels. Mainly they sell CDs of Swaggart's Southern Gospel music, or his books and study Bibles, in return for a donation. The on-screen calls to buy these are more akin to a Shopping Channel pitch, often one which is flawlessly dovetailed with a gospel presentation. What's perhaps most disturbing is how Swaggart can move so effortlessly from breaking down in tears at the reality of the gospel, to asking viewers to buy his new book or worship album.

There are many others. Rod Parsley – a prosperity preacher so slick and smooth that he can almost hypnotise you into picking up that phone and making that donation. The once-disgraced Peter Popoff, who'll send you a vial of 'Miracle Spring Water' for the low, low sum of $19.99, which will rid you – according to on-screen testimonials – of all financial debt. And of course, the daddy of them all, Benny Hinn, who mixes requests for 'seed-sowing' with borderline violent on-screen behaviour (knocking people down with the power of the Spirit, obviously) which the casual viewer must find somewhat distressing. This first-hand report from a Christian who attended one of Hinn's 'miracle healing' services is chilling.

The Bible is quite clear about all this stuff. 1 Timothy 6:3-10 comprehensively debunks the prosperity gospel, and a few phrases in particular stand out. In v5 Paul warns about '...men of corrupt mind, who have been robbed of the truth and think that Godliness is a means to financial gain', and in v9 he says that 'people who want to get rich fall into temptation and a trap and into many foolish and harmful desires that plunge men into ruin and destruction.' Famously he ends with that reminder that 'the love of money is the root of all kinds of evil.' The Bible isn't fuzzy on prosperity, and that out-of-context verse about 'a full measure, pressed down shaken together and running over' won't change that, no matter how compelling it might sound in the right accent.

So there are a few problems here. First, faithful people – and probably those with aspirations far higher than their moderate earnings – are being duped into giving money to a scam. Second, while this might not be the front door of the UK church, it's certainly the front lawn – the public face of the faith that millions of people are potentially exposed to whenever they take an intrigued wander through those high Sky channels. Perhaps even more concerning however, is the church's apparent indifference to it. There's a fire on this front lawn, and it's not a holy one. Yet for the most part we ignore it, write it off, imagine that while these 'preachers' aren't having a positive effect, the damage they're doing is minimal.

I simply don't believe that's true. While much, although not all, of this programming originates from America (where the seeds are all gratefully banked), it is having a profound effect on Christians and non-Christians alike here in the UK. We have to start caring about this; the TV networks must be called to account for inflicting this scandalous con-artistry on the unsuspecting faithful, and we have to realise the negative impact these programmes are going to have on our evangelism.

I might not have all the answers, but I don't think we should just stand by and watch this any more. Christian television has to put its house in order; to stop hiding behind the idea of 'breadth and diversity' when in reality it is taking money from 'ministries' which propagate heresy. That's how Christian TV works, in case it wasn't clear; these ministries pay for their slots on these channels, and then use that cost as a lever for further fundraising. The cause: 'Help us stay on the air and reach a billion souls', as GOD TV often puts it.

Churches need to debunk this teaching from the pulpit, and especially as part of our evangelism. And none of us, under any circumstances should find ourselves sowing a 'seed of faith.' To do so turns Christianity into a pyramid scheme, where the advancing Kingdom is replaced by the dream of material gain. 

Martin Saunders is a Contributing Editor for Christian Today as well as an author, screenwriter and the Deputy CEO of Youthscape. Follow him on Twitter @martinsaunders