Yeah, every single uni I applied for ended up having an interview/open day.
It was a while ago so I can't remember exact questions but it is quite standard and fairly logical:
"Why this course?"
"Why this university?"
"What part interests you the most?"
"What makes you think you'll be good?"
etc.
They'll ask about your personal statement, and then ask maybe one or two questions related to the subject, a few them asked a simple maths question (and helped you through it). It's really nothing to be worried about (although I was for my first one as I did not know what to expect (I remember looking up what all the professors were specialised in and rehearsing my answers on the train xD)).
The thing is, the interview for CS is really not a deal breaker. If you're getting an interview that means you're doing well and they are close to giving you an offer. The real purpose of the interview I came to find is much more about making you want to choose them over other unis (and it works as a tactic) rather than them deciding if they want you.
Advice for an interview for CS. or any uni based interview, is to simply talk and speak your opinion. Giving brief answers means you have to answer more questions and also gives nothing for them to work with as often it's just a conversation about your interests (and sometimes theirs). If you're really passionate about something just talk about it and enjoy it.
Personally, I found sometimes that the professor who was interviewing me was more shy than me! Being nervous is perfectly normal and they expect it, they don't want to see that you're a prodigy, they just want to see that you are interested in learning new things.
I always asked a question at the end of the interviews (and sometimes I got some really interesting answers). It's obviously optional but I think if you come up with a good question it's a quite nice for the professor to talk and a nice way to be remembered if you come back in September
Edit:
Thinking about it. If you're not going to take maths they will
definitely ask you to explain that/explain how you'll cope with the course. Definitely worth thinking about the answer beforehand e.g. :
"I wasn't able to take it at school as I realised I wanted to do CS after I could swap subjects. I believe though that I am capable of keeping up with the pace of the course. During my summer holidays I have taught myself AS maths and also I have read books related to the maths in computer science("quote books here"
. My favourite was X book for Y reason." *continue to talk about the books/what you've learnt*
That would be a fairly generic answer I can think of. Don't lie though. I'll say it again, you really do need to like maths for CS. Don't just talk the talk and not walk the walk. You should do some studying to justify your choices.