Year 12s: what will be the first way you research your future options? >>

Dropping out to change uni+course?

Hopefully I've given sufficient details below,
So, I'm currently a student at Imperial College London reading Physics, I started in 2010, finished my first year a few months ago, and now I'm taking a gap year between my 1st and 2nd year. And I have been thinking about what I want to do in the future, and was thinking of changing my course.
Due to mitigating circumstances such as family problems, and thinking of changing my course, my first year wasn't great, especially considering I want to enter a very competitive field later on in life.
I'm thinking of changing my course to study something like Economics, which I'll enjoy more, and find more relevant to my course.

I really don't know how universities see a dropped out student, and whether its frowned upon, especially since I'm thinking of applying to high ranking universities similar to Imperial, such as Oxford, LSE, Durham, St. Andrews and Warwick.

The time between now and if I reapply won't be wasted though, as I'll most likely have work experience in a barrister's chambers over the next two years, with the possibility of completing my Economics A-level and maybe taking up History as well.

Its standard to give out results on TSR so here they are:

A-level
Maths A*
Physics A*
Further Maths A
Chemistry A
Economics AS-level- A

GCSE's: A*A*AAAABBB, (Its pretty much A's in sciences, maths and english.

I know this is long winded, but I'd really like some advice, and I'd appreciate the hell out of anyone who reads and replies to this.

Thanks.