It depends on the time of year, since the two cities have opposite and overlapping daylight saving time schedules.From the last Sunday of March to the day before the first Sunday of April, when it's 8:30 AM BST in London, it's 6:30 PM AEDT in Sydney.From the first Sunday of April to the day before the first Sunday of October, when it's 8:30 AM BST in London, it's 5:30 PM AEST in Sydney.From the first Sunday of October to the day before the last Sunday of October, when it's 8:30 AM BST in London, it's 6:30 PM AEDT in Sydney.From the last Sunday of October to the day before the last Sunday of March, when it's 8:30 AM GMT in London, it's 7:30 PM AEDT in Sydney.