Hi Scott0710, and welcome to the forum.
The existing SCR Receiver only contains the wiring that controls the central heating. There are no wires present there for control of the hot water, so you cannot install the Hive receiver there and expect it to control the hot water.
The Hive receiver should replace the Danfoss programmer shown in your third picture. You will need the
dual channel version of the Hive for heating and hot water control.
The Danfoss programmer is wired as below:
And the Hive
dual channel version is wired exactly the same. Lucky you, they are a straight swap.
The SCR receiver shown in your first photo should be decommissioned. It cannot just be disconnected, otherwise the heating will be 'open circuit' and will not work. You need to trace the white cable shown in your first photo of the SCR receiver back to its origin at the wiring centre. Unfortunately not all wiring centres are the same and / or installed the same and I can't see the wires clearly enough in the photo to follow them with certainty to tell you which they are.
When you have found the other end of the cable, note where the Grey and Black wires are connected. Now disconnect all four cores of the cable and remove it from the wiring centre. Then insert a wire link between the two terminals where the Grey and Black wires came from thus joining them together. The SCR receiver backplate and the cable to it can then be discarded.
For future reference it is best if you start your own new post rather than tag it on the end of someone else's, doing so means that it could easily missed by most. This is also called hijacking and is against the
forum rules. Don't start another one now though, or you will have two threads going on the same topic, which gets very confusing, and is also against the rules.
EDIT:
Sorry, I didn't comment on:
I would like the wall mounted thermostat..... (photo 3 below) to be disconnected.
I didn't mention it, because it won't have any wires connected to it. It is linked by radio signal to the SCR and is battery operated, so once the Hive is up and running, just remove it.