Ok, well going on these replies, which replacement filter would you recommend. A standard one is £5 but if a replacement can give me a bit of extra noise (but not too much), maybe a bit more responsiveness and last forever then it's probably worth the extra £25.
Don't care about performance gains, I just want to get the most out of my car without modifying it as I'm not allowed and ideally I'm after value for money as well.
They all do them, K&N, ITG, Green-Cotton etc. etc. - which is best?