Right first of all, you need to learn the difference between earthing and bonding.
They are different things which do different jobs.
In a building you have some metallic 'things' entering the building from outside. These will include water pipes, gas pipes, structural steel and the electrical supply earth.
Each of these items may be at a different potential (voltage) to each other, which could present a shock hazard. We BOND all these items together so that they are all at the same potential, and can not present a hazard to people in the building.
You may have heard of a Faraday cage? Bonding works on the same principle.
Earthing is where you provide a path for fault current to flow to.
Lets use a washing machine as an example. If a washing machine is not earthed, and a fault occours with it that causes a live wire to come into contact with the metal casing of the machine, all that will happen is the casing will also become live and it will stay live. Anyone touching this machine will receive a shock. Obviously, that's a bad thing™.
If the casing of the washing machine was earthed, and the same live wire came into contact with it, a large current would flow in the circuit, and the fuse supplyingthe circuit will blow leaving the washer electrcically isolated, and safe to touch. No one gets a shock, everyones happy. This is known as automatic disconnection of supply.
As you can see, different things doing different jobs.
MET is Main Earth Terminal. It's the point where all the installation earths and the bonding wires all connect together.
The tray will probably be better off being earthed but with out seeing it, it's hard to say for sure.
If there is an existing installation in the building, the landlord has a duty to ensure it is safe regardless of whether he fitted it or not. If it's safe then not a problem. If it is unsafe he sould either put it right or have it removed.
Did you receive an EICR certificate to say the wiring complies with regulations when you rented the property?
