If I wanted to call Out of Hours doctor for gradual gum disease antibiotics.... ?

Gradual gum disease or gradual anything is not an emergency, so just wait until the dentist is open and phone the office. 

A dentist is the best person to ask about infected gums.  You may need a Regular Dr. who knows your medical history to consult with the dentist if there is a history of bad reactions to antibiotics.  I have had so many bad reactions - including life threatening.  I will always return to my family Dr. to have my records available when I need an antibiotic.  They are serious medicine with potential to harm as well as heal.

Usually you would require a visit to the dentist to help resolve gum disease.  Antibiotics may provide temporary relief but they usually won't solve the gum problem alone. Your best bet is to visit your dentist for a full exam. Good Luck!

Dentists are OPEN in the UK. You make a normal appointment and they decide if you need antibiotics. You do not need a Doctor.

You should live with it until morning.

They aren't going to give you antibiotics (or other medication) for this except during a regular appointment.  This is not an emergency for out of regular hours. 

You don’t. That’s your doctor’s job.

thats up to them to decide