Hi and thanks for the response.
Apple refers to sleep mode when using the smart cover.
Powering off is really quite inconvenient as it takes a while to power on again.
Airplane mode certainly works but again, this is a manual step just like turning cellular data on and off is.
To me it seems like Apple has made some rather odd design decisions in this area.
Having the device consuming 1 gig of data in 3 hours while in sleep mode is to me unacceptable.
It looks like the map application was updating while the iPad was in sleep mode.
I may have to learn to live with this flaw unless apple releases a proper fix.