What should I do in the summer between University and Sixth Form?

Firstly good luck with your A-Level results. Get some well-deserved rest and spend some time with family and friends. You ought to be well-rested once you hit the library at university.

If you want to do something though, a few ideas (no particular order) could be:

1) If possible, do a little part time work, even if unpaid or informal. For example if there's a local or family business, helping or shadowing the accounting / finance bits. Obviously this is very opportunistic and I wouldn't go looking for these.

2) Sounds like you want to do Spring Weeks. Apply early and apply broadly. To do that, perhaps you can get together the cover letters, which you can probably draft today. Without other distractions like lectures you can probably make them a little more bespoke.

3) Get a role / leadership position in a society, or found one, once you arrive at university - do some prep now to hit the ground running when you get there.

4) Network A LOT - try to find people who you have something in common with (same hometown, university, course, etc.) and be personal. Summer is generally a good time to network as bankers are typically less busy during the summer.

5) As far as summer courses go maybe look at WSO or BIWS - not a formal course as such, but something to educate and prepare you for assessment centres, and indicate some interest in the sector.

6) Find some extra-curricular (ideally, relevant) activities for yor CV

7) Start your own company. It doesn't need to be the next Apple (I mean it can be, but if it is then I'd re-evaluate your career goals). This could be as simple as the age-old lawn mowing, or ordering a bunch of stuff on Temu or Alibaba and selling it locally or even online, or doing a YouTube channel type thing. Just something entrepreneurial.

I probably forgot some things so hopefully others add.

Best of luck.