Assuming the Astra J chassis is the same, wheel arch size is the same, I have done a calculation based on changing my wheels to the ones you are considering and there isn't any problems. If you go to the same website you can compare your current wheels to the ones you are looking at...
http://www.wheel-size.com/calc/?wheel1=2...0mm&sr=0mm
http://www.wheel-size.com/calc/?wheel1=2...0mm&sr=0mm