Ah - OK.We will be getting a brand new consumer unit john, we would never keep that old thing. Yes the earth is staked outside, but we are running 2 10mm earth cables in for that.
That VO-ELCB (assuming that's what it is!) needs to go. If you still need an RCD there (see below) it could be replaced with that. Otherwise it could be replaced with an isolator (to make life easier for, say, the electrician who replaces the CU).
With the earth rod, you have a 'TT' installation. That means that every circuit in your installation needs RCD (or RCBO) protection. If the new CU is going to provide such protection to all circuits, then you don't need another RCD where that VO-ELCB is (so it could be replaced with an isolator). However, if there is going to be so much as one circuit that does not have RCD/RCBO protection, then you would have to have the VO-ELCB replaced with a ('time delayed', probably 100mA) RCD.
Kind Regards, John