Have you already applied? If so there is no point asking this question
But here is my opinion if you haven't. I can't say that without Further Maths your application looks exceptionally strong, and without a 3rd science (incl. Maths) you could be at a disadvantage (Economics is not a heavily weighted subject). However, if you want to go there, apply. You have a chance, there is no reason not to. I say this to a lot of people; if you even have a chance of getting into Oxbridge/Imperial, apply. Because even if you don't get those offers, you have 3 others, and since you are an Oxbridge candidate with A* predictions, you will very likely get them. There is very rarely a downside for such high achieving students to not apply (if they want to of course).