Where is the main earthing terminal?

That is the Suppliers earth connection. From this, the Earthing Conductor (nowadays, generally a 16mm cable in houses) goes to the Main Earthing Terminal.

Yes, the earth block inside your CU can be the Main Earthing Terminal, or you could have a block outside the Unit, all depends on access and room inside the CU/Fusebox.

Alan.

Well said Alan.

Not that well said! There were two questions, one being 'Is there any problem ...' and the other 'Is this specifically disallowed?' Alan says 'yes' then appears to suggest the approach that is both problematic and specifically disallowed. Where safety is involved, clarity of expression is essential.

I suppose I could make my question simpler too.

Is there anything, regulations wise, stopping me from connecting the gas and water pipes to the earth block in the consumer unit (10mm) and then connecting the earth block to the incoming main earth at the meter (16mm)? I think Alan's answer is yes but I'm worried that I can't find this method in the on-site guide or any other sources I've looked at.

I also intend to run just one (unbroken) 10mm wire to both the gas and water pipes as I believe this is allowed but is there any requirement as to which pipe it goes to first. Redading around seems to suggest it needs to go to the water pipe but I fail to see any difference in whichever one it goes to first.

There is nothing at all in the regs stopping you doing what you propose. In fact it is a very common way of doing things. In fact that is how this one is wired up

You can go to either pipe first!

If his answer is that there is something stopping you, then I'm not surprised you cannot find the method in an on-site guide :-)

Its perfectly acceptable to use the earth bus bar in the CU as the MET, and in fact is quite common. Many CUs will even come with marking indicating spaces on the earth bus bar for bonding conductors.

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