Apron Controllers don't need any formal qualification
Don't call them Apron Controllers, Marshallers or whatever, they get very upset. They are Airside Operations Personnel.
No you don't need any qualifications to get in. In fact you probably need more academic prowess to become a street cleansing technician than to get a job in Airside plOps.
Go for ATCO. At least your 5 A levels will serve you in good stead for that one. They'd be wasted on the other option.