Hi
I got the answer to my original query by emailing emirates directly
They told me the only way to buy flex tickets direct is not online as this always gives the cheapest fare to the fields entered
To buy flex I have to phone the reservations centre whose number for the uk is 0844 800 2777 which I did and found flex flights to joburg at Xmas are about £140 dearer than saver but giving full mileage.
This means we probably will be gold again next year as I'm willing to pay that much just so we don't have to queue at the airports.so thanks for all your views we got there in the end
Happy flying