'I'd like to emphasise, first of all we didn't work with Sir Alexander Fleming, I hardly knew him. Fleming's work was done ten years before the work in Oxford, but we just happened to to work on the substance that he discovered ...
'[Also, the penicillin research] was not done because of the war, it was started before the war. This is another things that's stated, that we did this because of the war. This is not true at all.' 
In 1929 Florey and his colleague, Dr Ernest Chain decided to focus their research on this Penicillin. They discovered how to produce an effective and safe antibacterial agent from the raw mould juice and designed mass production methods - painstaking and extremely difficult work.
In order to produce the raw mould juice, they had to grow huge amounts of the mould in order to extract the vitra broth that formed underneath it, which contained the Penicillin. It was not easy to keep the mould in a state that yielded the best results. Fortunately, Chain discovered that the process worked better on ice. Yet, after several months, they only had a single pinch of good quality Penicillin powder. This precious powder was tested on eight mice, with remarkable results, proving the effectiveness of Penicillin. Trials on humans were commenced soon after this breakthrough.
Meanwhile, the Second World War had started and the medical profession were in desperate need of an antibacterial drug. Thrilled with Florey and Chain's discovery, large scale production of Penicillin was called for. Unfortunately, British firms did not have the money nor facilities to help with large scale production, so in June 1941 Florey approached several American pharmaceutical firms. Seeing the potential of Penicillin, and having the resources to develop it, they accepted the challenge. Some pharmaceutical firms took out patents on the drug, and Florey lost control of his product and the income from future developments thereon. However, he was not overly concerned; he believed that getting the drug manufactured in large amounts was all that mattered.
Initially, supplies of Penicillin were restricted to the military, but it was not long before civilians were able to use it as well. Australians were the first people in the world to have general access to Penicillin: from 1944 onwards it was made at the Commonwealth Serum Laboratories in Melbourne.
Fleming, Chain and Florey were jointly awarded the Nobel Prize in Physiology or Medicine 1945 for this work.
 de Berg, Hazel, Transcript of Taped Interview with Lord Howard Florey, 5 April 1967, National Library of Australia, Canberra, p. 8 of 15.