Maths and Further Maths Watch
PS. I am Year 11 and dont know what to choose for A Levels
For Economics courses it varies a little, probably the most notable exception being the the Economics department at LSE (and hence all joint courses as well as single honours) do not accept them with one other subject only - citing "academic breadth" as the reason. If LSE Economics is your aim, then you should plan to take a 4th subject. For Oxbridge on the other hand I believe they're perfectly happy with it (certainly it's quite common for Cambridge Economics to have Maths/FM/other, often Economics). You would need to check other courses but on the whole I think universities outside of that realm are less likely to be picky provided you have some suitable mathematical preparation (which you will).
If you want to keep engineering as possibility, Maths, FM, and Physics would probably be the best option as it ensures you meet the requirements almost all courses (the only exceptions being some chemical or biomedical engineering courses may require chemistry/biology - although most chemE courses accept physics and teach you the chemistry once you start the degree). Taking Physics with double maths would also allow you to pursue Physics, and is useful for Maths and CS degrees. The former normally having at least some, and often much, applied maths/theoretical physics content, and for the latter some of the electronics background is slightly helpful early in the course (although this isn't really critical and FM would make more of a difference I think). It's also fine for most Economics courses (LSE excepted as above) as none I can think of require Economics at A-level.
Some unis look at maths and further maths as too similar and therefore may not count further maths unless you did 4 so they’d prefer you to do maths/physics and something else if you can only do 3.. depends on the uni; I’d have a look at ones you may want to go to