I am glad that Caroline Petrie is going back to work because, as far as I can tell, she is a dedicated and effective nurse. But I was disturbed by North Somerset Primary Care Trust's judgment.

Caroline Petrie was suspended without pay because, after changing a patient's dressing, she asked the elderly woman whether she would like her to pray for her. Although "taken aback", the patient did not complain but mentioned the upsetting event to others who then did so.

The trust ruled that Petrie had been acting in "the best interests of her patients", and I am sure she thought she was. I spoke to her a few days ago, for a discussion on the Jeremy Vine show. She was friendly and pleasant, happy to talk about what had happened, and completely unable to understand why her actions would upset people.

I know I would be upset if it happened to me. I was reminded of a recent taxi ride to the coach station in Bristol. My Muslim taxi driver was very friendly and we chatted all the way. As I got out he politely handed me my suitcase and said "May God go with you".

"No, no" I replied "I don't think he exists." and walked off feeling horribly confused at what I'd blurted out. After all, if there's no God how could the man's wishes do me any harm, and if they couldn't why should I want to upset him – wasn't I just as bad proselytising for atheism as he was for God. I got on my bus feeling a little churned up.

Now imagine (as the National Secular Society does) that instead of getting on a bus, I were ill, and completely at the mercy of a God-fearing nurse. I would experience a horrible conflict between speaking out for what I believe, not upsetting a kind nurse, being angry that she had upset me, and so on. This is not what you need when you are ill.

This is why North Somerset Primary Care Trust were right to take action in the first place and then to have a proper tribunal. What bothers me is the way they worded their judgment. First, they said that nurses did not have "to set aside their faith" while at work. I agree – but only because that's impossible; if you have true faith you can't suspend it 9 to 5. The problem occurs when someone pushes their faith onto someone else, and that is what Nurse Petrie seemed to be doing. Happily the NHS guidelines are quite clear. They state that "such behaviour, notwithstanding religious beliefs, could be construed as harassment under the disciplinary and grievance procedures."

Second, they acknowledged that "some people saw prayer as an integral part of healthcare", and that really bothered me. Perhaps they meant merely to state a fact, rather than condone it. Even so, I think they should have said that this is wrong. Prayer absolutely should not be an integral part of healthcare. Why not? Because healthcare needs to be effective, and that means basing it on evidence. We now have all the evidence we need to show that prayer is not effective, and even that telling someone you are going to pray for them can be harmful.

I say this on the basis of the largest and best controlled study of the effects of prayer. In the Harvard prayer experiment, 1802 cardiac bypass patients were divided into three groups. Two were told that they might be prayed for; half were and half weren't. The third group were told they would be prayed for and they were. The first two groups recovered equally well, but the group that knew they were being prayed for actually did worse. Perhaps their hopes were falsely raised, or perhaps they were upset to know that someone was praying for them. We don't know, but we can safely conclude that knowing you are being prayed for is not helpful.

Christian groups have complained that the ruling will "inhibit freedom of conscience". This is ridiculous. If a nurse's conscience tells her to pray for someone, then as long as the patient doesn't know about it, it can't do any harm. But if her conscience tells her to go out and spread the word of Jesus, or encourage others to join her in prayer, then she should read those guidelines: "you must not use your professional status to promote causes that are not related to health."

Some people may think that prayer should be an integral part of healthcare, but they are wrong. The guidelines are absolutely right.