Adding to Eddie's posts ................. assuming the box is inside (maybe the meter is outside) ....... then allow around £300 for a straight swap.
It may even be cheaper if there are only a few circuits. Cost may rise though if the surround has to be discarded because it's too small for the Consumer Unit.
Also..... 1972 wiring may well be perfectly Ok, but if the system hasn't been tested for 10 years, then it really should be done at the same time. This might add around £120 to the bill, but it will depend on whether he comes across any "horrors" that need amending.