I'm personally not applying for maths, but have a ridiculously ambitious friend who is applying for it at Cambridge, Warwick, Durham, Bath and Bristol - all very prestigious.
Also, I've heard that not doing Further Maths A2 can put you at a big disadvantage, so try and hang on to that.
I would agree with the 'hang on to the Further Maths A2' depending on where you're applying. I know that some unis give different offers based on double/AS FM/single maths and the higher ones want STEP/AEA if you don't have FM (Bath+).
For most top universities, Further maths is a requirement! You are so lucky you are being told this now, I was unaware that I needed it and am now having to do the full A level in one year. I would definitely say keep further maths! Really good ones would be the likes of Cambridge, Imperial and Warwick, which require you to have STEP. STEP is the reason I didn't apply to them I'm applying to UCL, Kings, Nottingham, Birmingham and Loughborough