Mark, technically fuel can be transferred between tanks - but only while on the ground.
Two procedures. The first is used by engineers, typically when using a fuel component, and requires total fuel content to be less than the capacity of a wing tank. For this procedure use is made of the refuel panel and its switches to move fuel from one tank to the other.
The second procedure would normally be used by the pilots if they have somehow ended up with more than the 680kg fuel asymmetry permitted between wing tanks, and utilises the centre tank transfer system. It is considerably slower than the procedure that uses the refuel panel (above).