Should I take further math at A level?

I got an A* at GCE O level in mathematics and am taking mathematics at A level and doing very well in it.I plan on doing engineering after school so should i take further maths?I've heard that its very very tough and it might leave less time to study for other subjects and it would effect them badly.So is it doable?I enjoy maths a lot and it is by far my best subject.However I do not know if I'll be able to get the required grade(A/A*) in it.Would universities like imperial college,MIT,Caltech,Cambridge give preference to a candidate with further maths?Could I have a good answer especially from someone who has done engineering or further maths at A level?Any suggestions would be really appreciated :)