Hey Sally
My view, and I haven't been tested on it yet, would be not to disclose my illness until I was in a position where the job was offered or the interview stage. But I'll be honest and say that I have only had to apply for one job when I was undergoing treatment and I disclosed my illness at interview stage. The employer, fortunately, liked me and gave me the job, waiving any concerns about time I may have off. I guess I may have been lucky but also think it's harder for someone to turn you down when they've looked you in the eye than on an application form. I also think job interviews are more about being liked by the employer than ability to do the job. A basic ability is essential but someone who is decent and likeable is going to win over a person with tons of qualifications and a bad attitude towards people (I hope!).
It also seems pretty unfair to have to disclose your illness on an application form. I mean, as well as disability maybe they should have tick boxes for "undergoing relationship breakdown" and "dream of travelling" or "addicted to illegal substances". In a work context these also strike me as kinds of dis-ability!
It is a moral dilemma, though. It sticks in the craw lying about your job history. I do understand your dilemma. I wish the law would come along to make it illegal for prospective employers to aske for disclosure of medical history on application forms. That would support the discrimination laws and prevent employers from exploiting this loophole. There's a difference between someone like you with a genuine case and someone who can't get out of bed in the morning. You deserve a chance to be heard and if the job application process doesn't allow that then maybe your need to make your own opportunity somehow. Maybe you could put the sick days down but appeal to their humanity by attaching an explanatory note concerning your illness. Or maybe just lie! What we need is a cancer patients union - i'm only half joking!
Anyway here's a DWP site on the disability discimination act. It may provide some interesting pointers although it's been dumbed down from when I first read it. There are some contacts on there who may be able to advise you better than me though! All the best to you.
www.dwp.gov.uk/employers/dda/who_covered.asp
Tim