Australia has a whole host of health risks, but as long as you are careful, you will be fine.
Reciprocal medical arrangements exist between Australia and the United Kingdom, which means that UK nationals may have unforeseen emergency medical treatment under the Australian Medicare scheme. Beware though - the reciprocal agreement has loads of exclusions and won't cover you for everything.
Protect yourself against mozzies - they can carry dengue fever and Ross River fever in Queensland and the Northern Territory, and Murray Valley encephalitis (which can be fatal) from Western Australia to Queensland. There are no vaccinations against these, but there are preventative measures.
Immunisation against yellow fever is essential if you're arriving in Australia within six days of having visited an infected country.
In 2009 and 2010 much of Australia experienced the worst whooping cough (pertussis) outbreak in many years. Babies are the main victims of the potentially fatal and highly infectious disease, because they are too young to be (fully) immunized. Thousands of cases have been confirmed. If you are travelling with an infant then looking into whooping cough preventative measures.
For more information check the Foreign and Commonwealth Office.
The number to call in an emergency is 000 (called 'triple zero' or 'triple oh') and can be dialled from any telephone in Australia free of charge. This number will connect you with emergency operators for the ambulance service, fire brigade or police. The first question that the operator will ask is which service you need.
If you have a mobile phone obtained outside Australia, using the universal emergency number 112 is a better idea. Using 112 will use any available network, will work even if your phone is not roaming, and will work even if the phone does not have a SIM.
You can call the police assistance line on (+61) 131 444.
If you require assistance during a flood, storm, cyclone, tsunami, earthquake or other natural disaster you can contact the State Emergency Service in each state (except for Northern Territory) on (+61) 132 500. You will be connected with your local unit and help can be organised from there.
Poisons information advice, who can also advise on snake, spider and insect bites, is available on (+61) 131 126.
If you have a road traffic accident or you want more information on road conditions you can call the Diver Emergency Network on (+61) 1800 088 200
Like in most countries opium, heroin, amphetamines (speed), cocaine, LSD, ecstasy and marijuana among other drugs are all illegal both to possess and to sell in Australia, with trafficking offences usually carrying a jail term. Users take drugs at their own risk. Foreigners should not expect more lenient treatment from police than locals.
The risks involved in taking or selling drugs in a foreign country far out-weigh the pleasure of taking them. It is easy to say, but our advice is 'just don't take em.'
Attempting to import illegal drugs into Australia is taken very seriously, and Australia has even co-operated with the police forces in Indonesia, Vietnam, Thailand and Singapore in intercepting drug traffickers arriving from or travelling through those countries despite those countries having the death penalty for trafficking. Even information on Australian citizens has been handed to foreign police to assist in trials leading to possible execution. Australia itself has long jail terms (up to life imprisonment) for drug importation.