Problems in using a metal consumner unit on a supply with TT earthing.
A TT supply typically has an earth impedance which is too high to cause fuses or other protective devices to operate in the even of a line-earth fault.
Traditionally either an insulated consumer unit was used, or a separate RCD in an insulated enclosure was installed before the consumer unit.
BS7671 17th edition Amendment 3 requires that consumer units and similar enclosures are 'non-combustible' i.e. steel, creating a problem of how to ensure adequate prtection when a TT supply is used.