Internships questions

It's most common that if you do an internship it will either be as a placement year (sometimes called a "sandwich year") between your 2nd and 3rd year, or as a new graduate. Summer placements do sometimes happen (sometimes after your first year, but more commonly after your second) but are usually a little harder to find and with less variety than the year-long ones.
Generally yes you do want to include your grades from your 1st and 2nd year on your CV when applying for internships but it might not play as big a role as say, any other relevant experience or a compelling cover letter. And "working at a high 2:1"(or equiv.) is sufficient, you probably don't need to list the specific % scores for each module, unless a module is particularly relevant to the job etc (and even then, i'd probably just talk about it in your cover letter...)
This is based on my experience, your mileage may vary lol. But in general that tends to be the case.
Make sure your course does support you doing a placement/sandwich year if that's something you're keen on (and how much that costs in fees, as that varies from university to university) and make yourself known to the team that oversees placement students (most universities will have one). Your university may also have a "job board" or opportunities for internal internships (working for the university or supporting on research etc). So it's worth seeking that out too.

Thankyou for the detailed reply!! My concern was that the 1st year has some modules I suspect i won’t be as good at, and although it won’t go towards mg degree, might affect internships. When you say ‘working at a 2:1’ do you mean the average of all your grades so far will get you a 2:1 if you continue? Or does it mean that your most recent grades (say only from the second year if you’re in your second year) are on track for a 2:1 (as only your 2nd/3rd year grades will count towards your degree)?

No worries Thanks for the extra info, that makes a lot of sense to me! Honestly, I think you could interpret it as either or, and as long as you're not lying - i.e. at your current trajectory you're likely to get a 2:1 at the end, there's sufficient evidence to support that, and you're upfront about it if they do ask you for more detailed information about your current grades (and honestly it's probably unlikely they will ask, unless it's for a module that's particularly relevant to the role) that will be fine.