Ucl program transfer

You would need to go through the process on portico to be considered by the new course. There's no guarantee they can consider you, but they won't rescind your existing offer for doing so.
Bear in mind HPE is offered by the School of Slavonic and Eastern European Studies, not UCL economics (or politics, or history). The modules are SSEES modules and there's a strong emphasis on Central and Eastern Europe accordingly. The economics side is also much less mathematical than the economics department courses.
This may or may not be what you're interested in, but it's important to understand and be aware of in case it's not.

Hi thank you so much for the reply. I phoned UCL admissions and they told me to fill in some queries form on their site and then apparently from there they’ll just reply with an email as to what else they might need from me and their decision. I might have interpreted what they said wrong though. Does that sound like what you would expect? Is the department they’re in separate from the faculty? Where i was looking it said that they’re both in the arts and humanities faculty.

That sounds about right. I thought it was through portico but they might've changed the process
Faculty is the overarching section of the uni, department is the specific academic unit providing your programme. For example SELCs, classics, and history of art are all under the Faculty of A&H. Obviously those departments are completely separate from each other and the degrees unrelated and separate (apart from joint honours). Generally faculty level factors don't matter to undergrads (there are some specific careers events tailored to the faculty of A&H for example but there are loads of general ones besides), it's more relevant for e.g. postgrad research students and academics where the faculty makes any difference.
Economics and philosophy is a joint honours degree between two departments - philosophy and economics. At UCL normally joint honours courses have a "home" department for administrative purposes, which in this case appears to be philosophy (which is part of the faculty of A&H but that's besides the point; economics however is in the faculty of social and historical sciences). The economics modules are furnished by the economics department.
HPE is not a joint honours degree between two departments though - it's all based in a single department (SSEES - also in the faculty of A&H but again it doesn't matter). The modules are all (with the exception of some history and language options) offered by SSEES. You don't take economics department modules on HPE - you take SSEES economics modules.

Hi thanks so much for the reply again. After reading what you said, I went back to look at the course and yeah the economics modules look vey different to what I would think it to be like. It’s very much based around Eastern European studies etc. I thought it might just be like PPE but with history instead of philosophy but PPE also seems to be a joint honours degree unlike HPE. I also want a career in investment baking in the future so a more quantitative degree is probably useful. I think econ and Phil is still a BA but all the compulsory modules are in econ so hopefully it doesn’t matter too much. Thanks so much again!

Yes this is the point I was trying to make sure you were aware of - as the course is based in SSEES and using SSEES modules, it's very focused on central and Eastern Europe! Which some people may be interested in but I suspect not everyone applying to the course is!
That said for investment banking your degree subject isn't really important - investment bankers don't use sophisticated mathematics, they just use a lot of basic GCSE level maths at large scales in spreadsheets frequently. So if you are specifically interested in Eastern Europe then it may be a course of interest. If you prefer the economics department modules though that's reasonable - they will be much more mathematical (as the SSEES ones don't assume A-level Maths to begin with, as those without the A-level do a maths module alongside those in first year in HPE to get them up to A-level standard, whereas the economics department modules I believe normally require A-level Maths and/or Further Maths from the start).
BA vs BSc is totally meaningless by the way - nobody, not employers nor anyone else, pays any attention to that.

Hey, can you tell me what they said? I'd also like to change course too

Hi they haven’t replied to me yet. They said they usually take up to 10 working days but since they were off from the 27th-4th it’s taking longer. What courses are you hoping to switch from and to?