Getting into IB with Economics degree?

Exactly, you dont need a degree in Accounting to become an accountant. This is why Im a bit unsure whether I should really go for Acc&Fin. I heard from some people thats its more like a 'vocational course'. But I was thinking that if I did AccFin, then I would probably do CIMA or ACCA afterwards.

Im not 100% sure with what I plan to do in the future. All I know is want to go into finance...possibly accounting. Thats why I've been thinking of Economics and Accounting. At least the Economics bit will keep my option open but if I decide to go for an Accounting Career, the Accounting bit of the course will give me some exemptions for the exam.

Do you know if top companies/employers see City University/Cass Business School as a good uni? I know City's ranking isnt that great but I've heard Cass is one of the top business school in the country.

Regarding CASS all I know is that it is good for post-graduate. I'm not sure about its undergraduate status. I do know it has arguably the best actuarial science Bsc.
What I'm saying is I actually think acc+fin from LSE, Warwick or maybe Durham will give you more options than Econ from CASS. You'll be targeted by IB and consultancy firms (and accountancy and finance is probably more related to this type of work compared to econ, not that it really matters), and have a slight short-cut route into accountancy. Neither of these is the case if you did econ at CASS I don't think.

First of all, Cass doesn't have any Economics courses. Economics is taught by the Econ Department which is not part of Cass. The merits of doing a course outside of Top 6 and getting a job in IB has been discussed extensively on here. If you can go into Top 6 (any course), I would do that instead. It appears that Cass is still a couple of notches below the Top Tier for Graduate Recruitment in IBs. However, that doesn't mean that it's impossible, but just harder. In the mean time, have a look at the graduate destination of the Cass Undergraduate courses.

http://www.city.ac.uk/careers/for-students-and-recent-graduates/destinations-of-city-graduates/cass-bursiness-school

Durham won't make a huge difference, Top 6 (Oxbridge/UCL/Imperial/LSE/Warwick). It might have a better reputation and pedigree than Cass, however that alone doesn't guarantee a top job.

Maths, Physics, Chemistry, Engineering, History, Politics, Economics.

Investment banks just want to know if you're smart. Getting a first or 2.1 in any of these subjects from a top uni will prove that.