I'm currently registered at Forest Hill Group Practise and called early Monday morning to make an appointment but was told they were booked up for the week! I was then told I could call this morning at 8 to get on the daily list, which I did but was told my situation wasn't urgent enough so I have to wait for a doctor to call me back later this week.
It just so happens that I am registered there too and having had no reason to see them for a couple of years, have had to make emergency appointments 3 times in the last 2 months. Whereas it used to be a bit of a mission getting an appointment, these last few times have been really easy - have actually spent longer waiting in the pharmacy for a prescription than entire time spent in the surgery. I was thinking they have clearly worked on this problem and got results!
Either you have been unlucky or you need to follow these tips: (a) phone at 0830 on the dot, (b) you need to be careful not to downplay the impact of your condition on the phone in order to get an urgent appointment.