I'm hoping some of the electricty regs gurus can help with advice on
meter tails.
Shortly I will be beginning an extension which forces a move of
electricity meter. I have all of the info about getting the meter
moved and where it can be located, but I cannot find any information
about the meter tails. What I need to know is the maximum length
allowed and what is / isn't acceptable for the routing of them.

Usually within 6 foot of the cutout on the same wall in my experience.
That does not include the meter being on the "other" side of the wall.

Is it acceptable to run the tails vertically through the cavity into
the ceiling void, horizontally for approximately 2 meters and then
out of the ceiling void into the consumer unit?

You might get away with it, but for that sort of run you might be
better using a switched fused isolator to provide a little more
protection (you`ll have to sort that out, RECs normally only supply a
straight on/off switch).

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