There is no legal requirement that calls for an existing electrical installation to be upgraded to current standards. However, there is a requirement under the Building Regulations for England and Wales to leave the installation and the building no worse in terms of the level of compliance with other applicable parts of Schedule 1 to the Building Regulations than before the work was undertaken. (Schedule 1 gives the requirements with which building work must comply)
Replacing a consumer unit in an existing installation is an addition or alteration to that installation. The work must therefore be designed, erected and verified in accordance with the requirements of the current edition of BS 7671, and must not impair the safety of the existing installation, and we adhere to all these regulations when we carryout our replacement works.