I've always done it with the earth wires from the cable into the socket and then one from there to the box. I don't believe that I've seen anything in the Wiring Regulations or even various guides on it. My thought would be that if you wire to the box and then to the socket, that if the wire from box to socket broke, that there is no earth at the socket. The other way round and two wires have to break to lose it completely.
I don't think that it's absolutely necessary to wire the washing machine separately, although as you are doing, it is useful to have the kitchen ring wired separately to the rest of the house. If you think that you might be likely to run a washing machine, a tumble dryer, a dishwasher and a kettle at the same time, I suppose you could run to the limit of a ring circuit, but diversity generally indicates that you are unlikely to run into trouble.
It is useful, perhaps, to run the freezer from a separate radial circuit with the breaker on the non RCD side of the consumer unit. This avoids the issue of an RCD trip compromising the freezer. It is probably a good idea to have the main kitchen circuit on the RCD protected side for a couple of reasons. a) It's an environment where water is being sloshed around and sockets may be close to sinks. b) depending on the house, you may be plugging in portable appliances that you use outside.
.andy
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