LSE/UCL/Oxbridge and AS grades

I wanna apply for economics/maths at universities like LSE and UCL, (maybe oxbridge we'll see..) and I do 4 alevels - maths, econ, chem and fm. my chem is honestly quite bad i averaged C/Bs throughout the year so I took the AS for it, and i'm worried I won't scrape an A. Just wondering whether these competitive unis really look at ur AS grades? Does it hinder your competitiveness compared to other applicants at all? Or should I worry more about trying to get A*/A in my other three mainly. I guess the answer's obvious, as in obviously strong A levels are VIP, but I just wanna know on a scale how important would AS grades be?