Almost anything is 'do-able. however, as I've said, particularly in the context of a 're-wire', I don't think that moving the CU would add much addituional complexity/work/cost.
"AIUI" is not an 'it' - it's an abbreviation/acronym for "As I understand it".
"DNO" is "Distribution Network Operator" - the organisation which supplies electricity to your property, and their responsibility extends only up to their 'service head' (with their own fuses), commonly called a 'cutout'. This is different from the 'Supplier' (the company who you pay for electricity) whose responsibility starts (and also more-or-less finishes) with the meter.
Fair enough - and, as I've said, I don't think the "3m" is of any great consequence, anyway. The electrician will decide on the appropriate type and route of the cables (and any other 'measures' required). Cables are, in general, not meant to be installed in wall cavities these days.
Kind Regards, John
