Records of Australian births, marriages and deaths go on a website today - giving many a clue to their family history on the other side of the world.
Ancestry.co.uk, the UK family history website, is launching the Australian birth, marriage and death indexes, featuring the records of almost 15 million Australians dating back more than 200 years to when modern Australia was settled in 1788, a spokesman for the website said.
He added: "Not only are these the definitive records needed by Australians to trace their heritage, but they are also essential for Britons wishing to discover ancestral links to the country.
"Family historians estimate that one in three of us have an Australian ancestor in our family tree, equating to around 18 million living Britons.
"However, approximately 11 million (60 per cent) of those with Australian ancestors know nothing about them."
Britain's close blood ties to Australia are the result of mass migration between the 18th and 20th centuries, when millions of Britons headed Down Under after the eastern coast was claimed as a British territory by Captain James Cook in 1770.
Most were free settlers who wished to escape the poverty and overcrowding of England and start a better life on what was literally the other side of the world.
High numbers of British convicts also arrived, with around 160,000 shipped off to Australia between 1788 and 1868 to ease Britain's overcrowded prisons.
The constant arrival of new free settlers and convicts caused Australia's population to swell from 53,000 in 1826 to 5.6 million by 1922, around half of whom were of British origin.
Famous names can be found in the records, including Australia's first Prime Minister Edmund Barton, Tasmanian born actor Errol Flynn and cricketer Sir Donald Bradman.
Ancestry.co.uk international content director Dan Jones said: "The addition of the Australian birth, marriage and death indexes will allow millions of Britons to uncover their lost Australian cousins and ancestors.
"It is incredible to think that as many as one in three Brits will have Aussie ancestors - and so probably also living Aussie relatives, meaning that this collection will be of relevance to so many of us."