Missing a week at the start of the first term of the first year?

I'm starting natural sciences this September, however I have my sisters wedding coming up in October which is going to be outside of the country. I would have to be gone for a week from the 5th October. Would I miss important things such as picking streams or would this have been done earlier? I'm unsure whether to go or not?

I really do not recommend that you do this. I'm not at UCL but missing a week at university regardless is generally a pretty bad idea - the pace is much faster than at school - and sounds like a particularly bad idea at the start of term.

Is the week in question freshers week? if so you may be better off asking your course leader directly. A wedding is a one off event so they may be able to make amendments.

Or you may find its when all health and safety inductions are done.

I'm starting natural sciences this September, however I have my sisters wedding coming up in October which is going to be outside of the country. I would have to be gone for a week from the 5th October. Would I miss important things such as picking streams or would this have been done earlier? I'm unsure whether to go or not?

I'd say it would be pretty disastrous. You should definitely talk to the uni first, because the presumption when people don't turn up at the start of the first term is that they aren't going to turn up, so you might find all sorts of things cancelled, you would be last on the list of course option selection and you'd miss all the introductory lectures setting out expectations, rules, sign ups, tips, reading advice etc etc. Unless you are an uber-confident socialiser you would find that the initial socialising events had been done, all the tours of libraries, union buildings, careers etc etc.

Check the exact dates you would need to travel, versus the exact dates (if you can get them) of the start of term activities, both the academics, accommodation and student union activities.

To get the dates would I just have to call the uni? Any specific department? I haven't found anything online other than either 18th or 24th September being my accommodation move-In date depending on where I end up. I'm aware there's no lectures during freshers so was worried about the week after as I wouldn't be there

That's half the problem, you won't be able to find that out until the week before at the earliest - everyone else is on summer holiday. It really is going to be very tricky. Basically, don't do it!

I'm starting natural sciences this September, however I have my sisters wedding coming up in October which is going to be outside of the country. I would have to be gone for a week from the 5th October. Would I miss important things such as picking streams or would this have been done earlier? I'm unsure whether to go or not?