Hmmm! Well my wife and I have been in Oz for 17 years.
We visited the UK for 5 weeks last September 2013.
I went to a GP walk-in clinic, because I picked up an infection, and was seen by Doctor (after a ten minute wait) and given a prescription for antibiotics.
The prescription was free because of my age.
Also had a dental check-up, x-ray and clean, at a local NHS dentist, for 18 pounds.
Many Australians travellers who are covered by Medicare in Australia, may be unaware that they are entitled to reciprical health care from a GP in the UK on the NHS.
You are entitled to be treated by a doctor as an NHS patient & the cost of the consultation & prescription medicine prescribed by the doctor will be covered by the NHS the same as if you are a UK Resident.
However, this does not apply to elective or non-emergency treatment.
More information is on the Medicare website.