Queries for University Application

I'm a student sitting for AS Level in June of this year. I currently take Maths, Economics, Physics, History. I am currently interested in doing Economics for Undergraduate, aiming for top universities in the UK and USA. With that in mind, may I ask:

1) I do not take Further Maths. How badly does it affect my chances for top universities in the UK and US (Ivy Leagues, Oxbridge, LSE, Warwick, etc.)? Because from what I've read, getting into LSE, Warwick, UCL, is quite tricky in my case. But I'm not so sure about Ivy League universities.

Thank you!