using the system back button from flutter driver

How can I use the system back button in an integration test?

So I'm using flutter and am writing integration tests, in most circumstances I can use the AppBar navigation, finding it by tool tip looks like this :

driver.tap(find.byTooltip('Back'));

But one of my tests opens a web page, after this opens I need to carry on with my tests which means I need to press the system back button, is this possible?

many thanks