If there are no internet appointments available with your preferred GP this means either he or she is on annual leave, or that all the available internet slots with your preferred GP have been already taken.
There are only a certain number of internet bookable slots available every day, so that those patients who do not have access to the internet are not disadvantaged and still have equal access to the doctors at the surgery. If you want to see a particular GP and no internet slots are available, please phone the surgery in the morning as you are still more than likely to be able to get an appointment on the day to see him or her.
You can download the User Guide to Online Appointments here