Although I am not depressed - I am merely someone who has experienced a depressing amount of depression - I have just completed eight weekly sessions of a cognitive behavioural therapy course, which is available on the NHS.

Big deal, you might well remark. But this course is unusual because I didn't have to leave my desk or even talk to another human being. The therapy is administered entirely by a computer programme. Beating the Blues is an attempt by the NHS to meet the growing demand for mental health treatment without spending a fortune on face-to-face therapy.

My instincts were against it - I was insulted by the idea that my difficulties could be solved online. So I logged on to my first session with some trepidation. I was introduced by a honey-voiced computer to five other "co-sufferers" - Andrew, Elaine, Jean, Bob and Heather - who were going to share my journey.

They were played by quite convincing actors, although their characters all seemed a bit feeble. I unkindly branded them as - to use a non-clinical term - "losers". They couldn't get a grip on their lives, they blamed themselves for everything, they couldn't take on goals, and they thought they were failures.

For me, depression is like a toxic black cloud that manifests from nowhere and wrecks my rational thought processes. Andrew and his cheerless bunch of pals just seemed browned off rather than properly depressed - unhappy as opposed to "ill". One couldn't control his school class, another had lost her confidence in finding a boyfriend, a third had let the house go to rack and ruin since her husband died. They were all unmotivated and had terribly low self-esteem - which I don't suffer from, even when depressed (my specialities are guilt and fear, specifically fear of madness).

But I tried to keep an open mind. The first 50-minute session examined the symptoms of depression and anxiety and gave a rough outline of cognitive behavioural therapy (CBT), which "rather than focusing on what happened in your past focuses on what is happening HERE and NOW ... It helps you to see the link between how you think and how you feel and behave."

The session explains how emotions are not simply results of events but of interpretations of events, which can, with proper training, be changed to be more helpful or realistic. It's not, it is emphasised, about "empty positive thinking", but about the distorted thoughts that depressed people tend to generate.

During the second session, I was taught to record my thoughts - in the hope that I could learn to change them - and also come up with some goals that were "positive, realistic, specific and measurable". The main thrust of the session, however, was to become conscious of "automatic thoughts", which "can become distorted and lead to anxiety and depression".

I tried to record these over the following week but found it difficult, mainly because a lot of my negative emotions don't seem to correlate with thoughts - at least, not thoughts that I am able to put into words. They are just moods, or reactions arising wordlessly out of the unconscious.

The third session focused on behaviour, suggesting that when you get upset you distract yourself through doing some physical activity - taking the dog for a walk, etc - or focusing on your breathing. It caught my attention properly for the first time in raising the topic of "Common Thinking Errors".

Common Thinking Errors included Black and White Thinking, in which you see everything in only two categories - all or nothing. If you think you haven't done something perfectly then you've failed, or if your clothes are less than immaculate you see yourself as a wreck. I recognised this tendency in myself - in some areas I am intractably perfectionist - and it came as a relief to have a label put on it as "distorted thinking" rather than "just me". It felt like the first step in getting it under control.

The other thinking errors - Jumping to Conclusions (negative conclusion when there is little or no evidence), Catastrophising (exaggerating your problems), Overgeneralising (thinking that if an unpleasant thing happened before it would happen again), and Should Statements (being a fierce task master who sets very high standards for themselves and others) - were less familiar in myself, but very familiar in some people I know.

The fourth session offered tools to counter these thinking errors. I was asked to find evidence both for and against my negative automatic thoughts (NATs). Empty positive thinking was discouraged - any challenge to NATs has to be based on evidence.

In session five, it was suggested that much of what we think is not conscious. It then tries to offer tools for digging out these unconscious beliefs. In psychology this is known as laddering and is a complex and skilled job. But the computer program suggests it can be achieved by anyone simply by asking repeatedly what your problem "means".

In the example the computer gives, Bob is asked to examine the thought "I'm going to lose my job" and ask "what does that mean to me?". "I'll have to start looking for another job," says Bob. What does that mean to him? "It will be hard to get a job - I'm not particularly skilled." What does that mean to him? "I'll have to take not very nice work." What does that mean? "I'll feel ashamed." Thus Bob has uncovered his secret belief that, "unless I have a job, I'll be a second-rate person."

This is all dubious to my mind. Without proper guidance, laddering can lead to all sorts of inaccurate conclusions, and the idea that the unconscious can be so simply and reliably accessed is questionable. After I completed the ladder, I uncovered the "belief" that I was "possibly damaged in childhood to the extent of being rendered unlovable". It was easy for me to recognise it as a false belief - but I'm not confident that knowing that is any help when this irrational feeling strikes me down.

More practically, I was asked to start writing down my successes on a weekly basis. It was pointed out that people who are depressed "give away" their successes, crediting them to luck or outside sources. Being asked to keep a success record seemed like a good way of reclaiming a positive awareness of yourself.

It was the final sessions, however, that had the most resonance. I was taught about how to recognise my "attributional style". This is how you go about putting together your world view - to put it simply, whether you are a glass half-full or glass half-empty person.

It then asks you to train yourself to tailor your interpretations according to whether what is happening to you is negative or positive. So if you win a game of tennis, for instance (which is the example they use) it is because "my serve is strong, I play well on all types of courts" - whereas a depressed person might just say "I was lucky," or that they just had a "good day". The idea is that you acquire the (to me, slightly disingenuous) trick of laying claim to your successes, and mitigating (or perhaps just rationalising away) the reasons for your failures.

I doubt that every situation is so crudely open to re-interpretation, but I can see that when you are depressed you can get into negative habits of thought that reinforce your depression, and a tool like this could be useful in countering it.

Obviously, being schooled by a computer has its drawbacks - you can't ask in the course of therapeutic conversation about anything you don't understand, and you often end up dealing with territory that isn't relevant to you. But it is not entirely impersonal - there is telephone backup if you require it.

I can't quite say that it "worked" - mainly because I wasn't depressed when I started it - but I have to concede that it is not as useless as I had imagined it would be. It is no substitute for a real face-to-face session with a counsellor, but in the absence of the necessary resources - and with some 10 million people reporting mental health problems - Beating the Blues is not an entirely worthless stab at countering an intractable problem.