Identifying function of electrical fittings
The green box in the far right is known as the &quot;cut out&quot; and is where the power enters the property. It contains the supplier's fuse.  The &quot;tails&quot; (wires) leave the top and enter a &quot;Henley block&quot;, which is essentially a big connector block.  From here the power is distributed to your three &quot;consumer units&quot;/fuse boxes.  The two brown ones on the left are likely from the 1970s, and the gray one with an RCD is a later addition that serves one or two circuits.  The cable leaving to bottom of that box is an armoured cable, most probably serving an outside, socket, shed or light.
The brown consumer units do not support RCDs.  Given that these are now mandatory in many situations, the gray box was probably added when someone needed a new circuit which needed an RCD.
If this were replaced and brought up to date all three consumer units and the Henley block would be replaced with a single modern consumer unit with RCD protection.
However, as others have noted the existing cables are in the wall which may limit the.options on where the new consumer unit would be placed.