packed to the brim?
UK:
Population - 60mill
Land area - 241,000 sq km
People/sqm - 249 aprox.
Aus:
Population - 21mill
Land area - 7,618,000
People/sqm - 2.76 aprox.
Certainly not all of Australia is habitable, but I am sure we can find more than 241,000 sqm of habitable land...