They aren't unguarded.
Apparently they never left.
Also, Britain isn't using their navy in Europe other than like, 30% of it plus the ones currently being made.
The two armies arrive and quickly push out the tiny bit of Japanese forces.
Assuming you got little reinforcements of course too, we basically sunk most of your cargo ships and reinforcements would have to go around Australia or go through the bits of the early blockade.
Remember, this is English turf. This is English home, we naturally have way more forces than you here.