The Standard Time Difference
Australian Eastern Standard Time (AEST) is UTC+10. When Sydney is on AEST (April to October, Australian winter), it is 10 hours ahead of GMT. When Sydney switches to AEDT (Australian Eastern Daylight Time, UTC+11) from October to April, the gap grows to 11 hours ahead of GMT. During UK summer when London is on BST (UTC+1), AEST is only 9 hours ahead.
The Seasonal Flip Problem
The unique challenge with Sydney-London scheduling is that Australia's seasons are reversed. Sydney is hottest (and on daylight saving time) from October to April — exactly when London is on standard GMT. And Sydney switches back to standard AEST just as Europe moves to summer time. This means the offset between Sydney and London can vary between 9 and 11 hours across the year.
Sydney to London Conversion Table
8:00 AM Sydney (AEST) = 10:00 PM London (GMT, previous day) | 12:00 PM Sydney = 2:00 AM London | 5:00 PM Sydney = 7:00 AM London | 8:00 PM Sydney = 10:00 AM London | 11:00 PM Sydney = 1:00 PM London
Best Meeting Times for Sydney and London
When Sydney is on AEST (UTC+10) and London is on GMT (UTC+0): 5:00–8:00 PM Sydney / 7:00–10:00 AM London works reasonably well. London is in early business hours and Sydney is wrapping up the day. The earlier Sydney morning hours (8–10 AM) correspond to 10 PM–midnight London — after hours for UK colleagues. Early evening Sydney is the most practical overlap.