A consumer unit is effectively the main part of any install, where safety is concerned. The safety devices have evolved greatly over the years and offer almost faultless protection to yourself from risk of shock. We now only fit full RCBO boards with surge protection as we believe the benefit of only losing one circuit in the event of a fault occuring greatly outweighs the slight extra cost in comparison to a dual RCD board.
Also, if you are looking to get an EICR (sometimes called a "landlord electrical check") then you will find that you will need additional protection (in the form of RCD/RCBO) to circuits supplying or passing through a special location (bathroom circuits including lighting, heaters, shower etc) and circuits supplying sockets with the potential to be used outside (arguably all sockets in a 2 storey building). If your old board does not meet this requirement then you will almost certainly need an upgrade to comply with regulations, not to mention to greatly add to the safety of your tenants.
