YY Sidge
I'm not in a GP surgery but I have my appointments booked.
I'm there 50-60 minutes before my first appointment to set up, get notes, read them.
If a patient is late I give them 10 minutes then get the next person- though there's no guarentee the next person is there.
Some patients do take ages to get ready, I need to assist with removable and replacement of shoes and socks.(And why do people wear tights under trousers when they know they need bare feet) 
Some people have family bringing them.Or taxi .Or Dial-a-Ride.
One patient in a wheelchair wheeled a load of dogs' pooh over my floor -nice. I had to clean that before the next patient. And sometimes I need a bit of airfreshener and a bloody good scrub of the chair extra alchohol wipes.
Our HA has a 10 minutes leeway- it's our discretion if we see them after 10 minutes.
TBH I'll see a late patient if it's physically possible.
But I might only be in a clinic for the morning. I have to get my daughter after school.
I've had patients turn up 2 hours late. One 6 hours late. And expect to be seen.
Their arguement is "Well I always have to wait". Yes, because I might have a patient who takes longer. I'm not drinking tea.
I'd love to say "Oh if I'm running late, you can refuse to see me" but I'd get cats-bum face.
And if I see a late patient and they don't acknowledge their lateness, then I say "Some of my collegues will refuse point blank.For any reason. " (Bet their blardy clinics run on time) 