Actually, I would slightly disagree with some points in the offered answer. While you could, as per the other answer, prepare for a "standard test that you can actually teach, speak clearly, prepare class material", I think you might give a better impression if you show that you have tried adapting your delivery to the specific requirements of the institution you are applying to.
Following the link you included, and looking under "Structure" (of the BSc in Computer Science), I find that students have Programming in Java in Year 1, followed by Programming in C++ in Year 2. I would assume that stage 2 means Year 2, and would prepare something that follows their general description of Year 2 programming module:
Programming in C++ (15 Credits)
The module focuses on introducing some basic aspects of the C++ language in a gradual manner so as to allow students to use it with confidence in follow-up modules and in their professional career.
For the topic, I would try to connect to their programme:
- Stick to the programming language and concepts from the module description: a basic C++ concept (maybe pointers maybe exemplified with a linked list?)
- However, they have a separate module called "Data Structures and Algorithms". You can show that you are aware of this by referencing something they have learned on a different module (e.g. those linked lists).
- In their first year, they had "Programming in Java" (for twice the credits). So compare and contrast with that: talk about how linked lists are implemented in a language they should already be proficient (well, familiar...) with.
For teaching practices, you need to make sure your example presentation covers the requirements they set to you with saying "200 Computer Science stage 2 Undergraduate students in their fifth week of term":
- There are 200 students in this class. Show how you teach a big class. (And then speak about the techniques you relied on in the discussion.) A standard follow-up question might be "And how would you change your delivery if the class had only 50 or 20 students?"
- They are in their midway through their term. You should take this into account in your delivery, by referencing, or even better, interacting with the "students" about past lecture material (similar to some points above).
- Most UK Universities are really keen on having interactivity in their lectures (rather than the dry "I talk you listen" lecture) anyway, so I'm repeating this point separately.
Finally, on role-playing:
- You might be expected to role-play and pretend your committee are students. I have friends that totally get into it, while I cringe at the thought of treating a committee member as a student, even for a minute.
- Best advice I got for how to cope with this is to "break the 4th wall", and instead of role-playing, announce "I would now ask the students for an answer, wait for a minute to let them think and pick somebody to attempt an answer" (or something similar).
- But if you can get into it, use it. You have a 5-minute slot where you need to discuss "why your chosen teaching approach was right for this cohort". You could pretend you have a great cohort (probably boring) or a cohort that has shaky basic knowledge (due to a covid year?), or a cohort not used to public speaking (again, due to covid?), tailor your approach specifically to your pretend-flavour of cohort and explain it in your discussion.
Terminology note: in the UK system, a course is usually a whole study programme (BSc in Computer Science) while a student will take a number of different modules in a semester (e.g. Programming and Data Structures are often considered "core modules").
Additional note on the topic: depending on the teaching load at the institution you are applying at (and some UK Universities have quite a high one), the institution often values the ability (and willingness) to deliver "core modules" in addition to specialised modules from one's own field of expertise. They won't hire somebody developing the next C++ standard to teach the students programming. And consequently, as most staff is expected to be somewhat familiar with the content of most "core modules", they also tend to be the easiest to target in interview presentations.
Good luck with your preparation and interview.
