You should check the rules based on what you are booking. At the top of the fare column, click on the 'Flex' hyperlink and it will show you the cancellation penalty
Checking one flex fare at random for UK-AU it states
Originally Posted by fare rules
]Cancellation (including no show)
Except where no show fee applies:
Before departure:
Full refund
so indicates a full refund. The Saver fare omn the same route shows a GBP200 cancellation penalty
I would expect that this will be the same on other days/routes , but check the rules to be sure