Totally disagree. While I'd be happy with crimps + heatshrink to extend cables to a new CU, it's still not ideal as it adds a concealed joint in the circuit. I would consider replacing the wiring up to the first point in the circuit to be best practice, and it shouldn't be all too difficult to do so for at least the lighting circuits at minimum.
In fact, while extending the ring final and altering the lighting circuit at my parent's house to accommodate an office being converted into a bedroom, I'm also rewiring large portions of the circuit(s) outside the room in order to remove excessive JBs. Said junctions are located in the loft and not concealed, but there are at least 10 of them up there on various circuits, and I don't consider them to be the hallmark of a decent electrician when they can easily be avoided.
I discovered one up there today on the lighting circuit with 10 incoming T+E cables, 30A JB, with loop in/out on the 30A terminals and various other outgoing connections to light fittings in pieces of terminal block shoved into the box. Credit to the guy that did it, it must have been no trivial task to get the lid on with all that in there, but he managed it. This has now been replaced with loop in/out at the switch, and it only cost a bit of time and a few metres of cable.
Oh, and two of the (previously live) cables in there turned out to be dead ends, simply taped up and left hanging in the loft. It really wouldn't have been difficult to remove them when they became redundant...
