If the cable is < 50 mm from surface then it requires additional protection in the form of
A 30mA rcd
B cable has sufficient mechanical protection covering it (3mm plate steel)
C cable is installed in earthed metal containment (conduit or trunking)
D cable has an earthed metal covering such as swa which can withstand fault currents from being Penitrated by nails and screws.
If cable is buried in a wall with metal parts other than screws then depth is irrelevant and cable must be protected by options A-D
As the cable is exiting to cu and it would cause major disruption to do either of the options then I would personally just make a remark on the test certificate
As has already been covered by the other lads posts bonding is something that needs considering as already said the cpc in 16mm will be 6mm.
Only really acceptable if it's a TN-S system or TT.