An installation has one MET.
The initials stand for Main Earth Terminal.
An installation may have EMTs (Earth Marhshaling Terminals) as well as an MET, but there is no requirement to have any.
All circuits of a location containing a swimming pool, are now (just as with locations containing baths or showers) required to be provided with 30mA RCD protection.
Depending upon where the board is situated, it may be that the circuit supplying the board would also require 30mA RCD protection.
However as the requirements are retrospective, it could be argued that a lack of RCD protection, would only Warrent a code C3, if the installation complied at the time of it's design/construction.