Neurology

What are the different routes to becoming a neurologist ?

Qualify as a doctor, complete FY1, FY2, IMT, then neurology specialty training. Complete relevant exams (MRCP and neurology SCE) along the way.
Separate route for paediatric neurology via paeds specialty training.

What if I do biomed first ?

Then you do 3 years biomed first, then 4 years grad med, then the many many years with of training set out by Democracy above. To get into grad med is more competitive than undergrad med and way more expensive. Speciality training after Foundation years is ever more competition.
It’s a very specific ambition to have to start a medicine career with.
More generally, have you had a look to see the differently focussed career options with a Neuroscience / cognitive neuroscience degree rather than aiming for medical neurology and limited to paeds.

What if I do biomed first ?

Doesn't cancel out anything I wrote but graduate entry medicine is even more competitive than standard entry medicine as pointed out above 😛 I would suggest A level resits or even studying abroad rather than going down the biomed route.