So, its a TN-S system. The gas meters are all lined up one after another, but there is no earth within the 600mm. Its actually connected from just when it leaves the basement (they are all like that).
So what I did, is run my 10mm earth from "our" side of the gas meter to the MET.
The water though (there is only one water mains into the building), is on the other side of the basement, access ok, but again no earth. So again, I ran a 10mm earth from "our" side of the water to the MET. The gas is approx 2.5 meters from the MET and the water approx 3 meters from the MET.