Having finally decided what we're going to do with the downstairs area,
we're going to have to move the consumer unit by about 4 foot. I wish
I'd thought of this scenario when rewiring :-(

Some of the circuits I'll be able to simply replace the last leg of
cable (from CU back to first socket), while others I'll have to extend
the cables.

I've read all previous threads on this, but haven't come across an
answer to this query:

Where I have a ring, with two 2.5mm cables going to the CU, instead of
extending each of the two 2.5mm cables, can I just join them up and
connect to the CU using a single 6mm cable? Anyone see a problem with this?

Just to make sure I'm being clear, the two ends of the ring, currently
both ending up in the CU, would instead both go into a 30A junction box.
Then a 6mm cable would leave the juntion box and connect to the CU.

TIA

--
Grunff