How to ensure safety of the wiring layout to a 20ft metal container

[sidekick]

The attached diagram shows how a 20ft metal container is currently wired. All swa (2.5mm 3c) is buried under new tarmac drive.
My questions is how can I ensure this is safe with no way of getting any new cables back to the house.
Is the RCBO at the house consumer unit along with the cpc earth via the swa cables safe enough considering this is a large metal box.
Or should the container be on its own TT (currently only a 13a supply from gate) ?

 

[Rockingit]

Do you have an option to long lead from the container back to the MET to see if you get a continuity reading?

 

[sidekick]

Do you have an option to long lead from the container back to the MET to see if you get a continuity reading?

Yes, only to the consumer unit as the earth rod appears to have been concreted over.
All tested ok and tested at the gate socket which the container feed is from.
Just not sure if it would need its own earth rod as any break in the earth along the extended route from the main house may leave the container in a dangerous state if under a fault condition