When the 13A sockets were designed, the teams had in mind that a "big" load would be a 3-bar electrc fire, and "obviously" you wouldn't expect anyone to have two of them next to each other. At the time tumble driers were unheard of, as were dishwashers, and few loads exceeded 10Amps.
Today, lots of people have a cluster of big appliances in their kitchens and utility rooms - a washing machine, a tumble drier and a dishwasher, a fast electric kettle, maybe a combination microwave and single oven that doesn't ned a CCU, so I'm reluctantly coming to the view that, for kitchens at least, the ring circuit and double socket may no longer be the perfect solution. Personally I've always put big appliances on their own switch and socket, on the grounds that, by size and weight, they are practically fixed; and my utility room has my well-known array of single sockets in vast numbers.
Though I have my doubts about a good-quality double socket being able to cope, as most loads are intermittent.