I'm quite shocked by this. First, they're isolating you and outnumbering you, putting you in a difficult situation; then they're doing parlour tricks, which no self-respecting Christian should be doing. Even if they believe what they say they are doing, it's part of no version of Christianity that I've come across that you can channel information directly from God, on demand.
That said, I'm also surprised to find you believing that spirits or the dead can communicate.
Maybe not "on demand", but I'm afraid this isn't uncommon. It's a fairly typical aspect of Charismatic Christianity, which Holy Trinity Brompton (HTB) are heavily into. The idea is that the Spirit speaks to us and guides us to truth, if we just ask. There's a theoretical acceptance that it's subject to God's Will, but in practice, it tends to become "pray, and God will speak to you". I've heard very senior and well-respected Christians in these circles talking about far stranger practices than this.
I was asked to offer my thoughts on Alpha, but I've been terribly busy recently, which has kept me from doing so until now.
I've previously written about the course, based on when I attended it as a believer, but I hope I can do better than a linkdump, so I've waited until I had the time to compose a proper summary.
First, it's not easy to talk about the Alpha Course without further qualification. There's a standard course template, which Nicky Gumbel tries to ensure no one deviates from, but courses vary massively, despite the Charismatic Evangelical slant of HTB themselves. Some courses are heavy on the Bible-thumping and Christian-flavoured woo, some are very wishy-washy with lots of liberal relativism, syncretism and chin-stroking. The former are nearer to the HTB model, the latter are nearer to how it's advertised as "Exploring the meaning of life". Therein lies the problem. My experience involved talks played directly from HTB's own videos as the centre of each week, so I expect it's about as close as you can get to a normal course without going to HTB, but other courses will vary.
The other interesting source for finding out about Alpha is the course leader's handbook. I once had one of these, picked up second hand, But I got rid of it long ago. I wish I'd kept it now, because it exposes some interesting tricks that are used. The approach advocated by HTB is to seed the group with plenty of sound believers, who can guide discussion in the right direction. But you don't give all the answers right away - that would look dodgy! The first 2 or 3 weeks are basic introductory stuff, covering some unremarkable topics, and the intention is to let the group run where they feel like in the subsequent discussion. I heard all kinds of crazy stuff in those discussions. After that, the idea of right answers is introduced, and the course becomes a lot more prescriptive.
I noticed a very distinct change in tone when the Bible was introduced, and Gumbel argued (in effect) that there are a lot of old Biblical manuscripts, therefore Jesus existed and everything the Bible says is entirely accurate. He does it with more finesse - it's a fairly nifty bait-and-switch in the video - but that's pretty much his argument. From that point, the "wrong" answers in the following discussion start to be knocked down with "the Bible says..." and the True Believers start to make a lot more noise about the right answers. From open discussion to Sunday School in just a few sessions!
If you stick it out through this fairly major hurdle (and I probably only found it quite so glaring because this was an area of particular interest and concern to me at the time), the next big step, another few weeks down the line, is the Holy Spirit Weekend. This is all about learning about and encountering the third person of the Trinity, and it gives the lie to zooterkin's surprise, because it's built around the expectation (though generally unstated) that you
will have an experience. This is where the rubber hits the road, and where they hope to give you the endorphin rush that will turn intellectual interest into emotional attachment. It's a weekend away for two reasons - to weed out those who aren't interested enough to make the commitment and who might therefore disturb the dutifully expectant atmosphere, and to allow enough time to create that atmosphere.
So you go away, you learn about What The Bible Says About The Holy Spirit (that early session on the Bible proves very useful here), and you have lots of time for the practicals, which typically consist of prayer in small groups, laying on of hands, and singing in tongues. By the end of several sessions of this, with other people helpfully delivering to order, it's a strong person who doesn't even feel a slight emotional reaction. From the church's point of view, it's all about the results. You could speak a nonsense language, fall down flat or just be filled with a sense of peace - the important thing is that you're hooked. After that, the course is just about keeping hold of the people who got something out of the weekend, and getting them to church.
I should say that some of the above reads as if there is devious intent where there may be none. Just as psychics can genuinely believe that they have a gift, people at any level of the process (even Gumbel himself) may believe that this is just what works for reasons that they don't understand, putting it down to God. Even arguments with gaping holes in them may be advanced in good faith, or simplified for reasons of audience or time available. I accept that there may be no intent to manipulate, and many courses do some or all of this differently. But I find it noteworthy that so many obviously manipulative techniques appear in the official HTB course.
I should also say that I attended this course about 10 years ago now, and while there are many moments that seem very vivid in my mind, it would be rash to claim that my memory is an objective record of what happened, or that I'm an impartial witness. All I can say is that this is my impression of the course, much of this is in line with other high-profile criticisms of the course, and some comes from sources which could be tracked down if necessary. But I think it's valuable, because I attended back when I believed, I wasn't looking for things to criticise, and the course probably caused more doubts in my mind.