What is the difference between a rewire and a consumer unit replacement?

A consumer unit (fuse board) replacement upgrades only the distribution unit — the box on the wall — and the connection point for your circuits. A rewire replaces all the cables throughout the property. If your wiring is old (rubber-insulated, aluminium, or T&E older than 25 years) a rewire may be needed. An EICR will identify which is required.