If you have a modern meter and switch, you can combine the consumer
units
(assuming you can get one with enough ways) by adding a beefy contactor
controlled by the "economy" output, but powering the things from the
full
time outlet.

Or you could get a dual tarriff consumer unit, it is basically two
units in one. You need to run a set of meter tails in for the 24hr and
E7 tarriffs but you don't need to add the expense of contactors and
such like, (also another maintenance issue).
Also, modern meters wouldn't need then I can't see why you would need
the contactor. The meter does that part of the switching anyway.

Thanks guys. I think this is over my head so i will have somebody do it. I
will then re-wire the household circuits as necessary.

Thanks again, Martin.