I will add a few points in addition to others concerns of exposed single insulated cables.
You tell us the supply is TN but what I was getting at is whether is is TNS or TNCS, this can matter, it may mean you garage requires equipotential bonding installed or isolation from electrical earth and rodding as a TT set up.
-Do you have a metal structure or support to the garage that is attached to the ground?
-Do you have any metallic pipes like service pipes (gas - water) coming up through the ground into the garage?
If the answer is yes to any of these questions then you may need to take specific measures in your earthing arrangements in the garage.
To note here that this will not be a concern if the garage is structurally part of the house and not a separate entity away from the house itself.