If they state you need a 6 in GCSE maths and apply without it, you will be automatically rejected. GCSE requirements for maths and English language are normally "hard" requirements.
Even medical schools that don't score GCSEs normally have minimum requirements (e.g. UCL, Imperial).
You should probably aim to resit the GCSE Maths to bring it up to a 6 as many have that as a requirement - if you limit your choices by those which will accept just a 5 in GCSE Maths I suspect you'll have very few options once you adjust for other factors as well.