Bit of background. I've applied for a job internally, which said "an understanding of X would be useful." I have six years experience of X - it's a very, very specialised field and I think there would be very few people who had this experience. I was rejected, (didn't even get an interview) and the email said "Others had more experience in X than you did."
So legally, can they turn me down (apart from the fact that they've ignored my experience in the field) for a job, stating I don't have experience in something that wasn't advertised as being mandatory in the job description?