CPS Homes interview questions

I was sent an email asking me to an interview. I went along and it was a very hard interview. I don't mind that so much, because I expect to be given a bit of a grilling at an interview. However, the interviewer asked me about my previous sick record which is illegal. I only found this out when I started working somewhere else from another manager. And I checked on the .gov website and it is. An employer can ask you about sickness and health after they have offered you the job incase they need to make reasonable adjustments or incase you can't actually do the job. But they shouldn't ask you BEFORE the offer of employment, otherwise this counts as discrimination as they could be basing their decision on your health, including your previous health which may not even be relevant anymore.