There's no specific requirement for the unit to be near the door. I agree with Trumpy that extending every cable to the new location with junctions is going to make it rather ugly, although likely to be quite acceptable from a technical point of view (there's just a
slight chance that the extra cable length might increase voltage drop beyond limits on some circuits, but most unlikely in an average domestic system if you're extending by only a few feet).
If you're lucky, some of the cable may take off in the direction you intend to move the panel (either in the garage or in the house on the other side of the wall), in which case you might be able to reroute and shorten them.
10 mm (I think) go from the isolator to the consumer unit
If these are feeding the whole house, I would hope they're larger than that. 16 or 25mm would be the norm, depending upon the main service/fuse rating.
