FrodoOne

What a pity that Jonno80 does not reside in New Zealand! He could then look-up the New Zealand "OWNER/OCCUPIERS ELECTRICAL WIRING WORK IN DOMESTIC INSTALLATIONS" to see that which he could do in a country which operates with the same "Standards" as Australia but is not so constrained by "restrictions", imposed - for the possible "benefit" of certain "organisations". Of course, while in New Zealand an "Owner/Occupier" is allowed to do certain things, it is then required that these...

Cut off the existing plug and connect the Bayonet Adapter Plug, which you have illustrated. Otherwise, make up a "lead" with a Bayonet Adapter Plug on one end and a "normal" Australian three pin socket on the other (using only the Active and Neutral conductors) between them. (The latter is basically that which Jonno80 wrote, but he added a few necessary caveats.)

And make sure that all metal parts of the "shed" are "bonded" together.

That which you have termed as a GPO is now more properly termed a "Socket Outlet". AS/NZS 3000 4.4.2.1 (Accessibility) states : - "Each socket-outlet shall be installed so that any plug intended to be used with the socket-outlet can be conveniently inserted and withdrawn and not cause damage to any flexible cord or cable connected to the plug. Socket-outlets shall not be installed where the withdrawal of a plug from the socket-outlet is restricted by a permanent fixture or fitting within...

Which I would say (from experience) would be having the "mid line" of the Socket Outlet not less than 150 mm above the bench. (You might get away with 100 mm - but ????) However, while it may look "silly", you could install a "normal (horizontal)" Socket Outlet "sideways"