Looking forward to suggestions to solution as my Daughters Corsa is exactly the same!!

Robin the Technician - i fix,therefore i am

First, check that the hvac is taking in fresh air from outside and not recirculating the air inside. Check that whatever mechanism switches between the two modes is working correctly.

Check that the air recirculation button on the dash isn't pressed, this will stop fresh air getting into the car and cause your windows to steam up, a blocked pollen filter (if fitted) will have the same effect.

As the other poster mentioned Corsa's also leak rain water into the front footwells from the bulkhead which will cause terrible condensation overnight, press your fist into the front carpet and see if it's wet.