Hello, I am Dr Helen, a UK doctor.
I am sorry to hear your son is unwell and agree that he needs to be checked by a doctor.
The easiest way to have him seen would be to go to an A&E department (Accident and Emergency) in your nearest hospital. They will have all the necessary staff and facilities.
From Golders Green your nearest two hospitals are:
The Royal Free Hospital
020 7794 0500
The Whittington Hospital
Tel: 020 7272 3070
If you don't have transport, any local taxi driver will know where these hospitals are.
Both these are NHS hospitals and are open 24 hours a day.
Take your Insurance documents with you. There should be no problems with you being seen in an NHS hospital and, especially as it is a Saturday, it would take longer to try and access medical care through other sources.
I hope he is soon feeling better.
I joined JustAnswer in June 2013 and am a UK doctor. I have been qualified for 23 years and have widespread experience in GP and cancer care.