Despite the ethical issues that some people have, I think that exploiting animals would be a necessary part of keeping mass society going sustainably on a crowded island in the North Atlantic.
We would need leather and wool as well as flax and hemp to provide textiles without the synthetic materials produced by heavy oil based industry.
Chicken tractors and pigs could eat domestic waste and plow our allotements and small holdings. Horse could deliver copiced wood pellets to our suburban combined heat and power boilers as well as doing other labour when biodiesel and autocomponents are in short supply.
Male animals are generally more agressive and less productive members of the community so most boars and cocks would end up in the pot at an early age.
Some of the methane from animal and vegetable waste could be trapped to produce biogas before the waste was composted.
I think the arguments against eating meat on sustainability grounds are missdirected. Industrial agriculture rather than meat eating is the problem. Small scale, localised polyculture food production is the solution. The problem is that this is out of step with capitalism and it is labour intensive even with horses, donkeys, ponys, chickens and pigs doing alot of the hard work. For such a system to work the population would probably need to be more spred out in low lying agricultural land. I like to imagine that we could create a network of ecovillage suburbs along existing transport infrastructure. The per hectare yield from allotements, and small holdings using techniques like forest gardening can far exceed that of industrial farming. If we could produce enough truely local food in this way, hill farms might fall by the way creating the opportunity to restore ancient woodland in our highlands.
Of course if you value an animal for its wool, eggs, milk or labour you might think twice about killing it, and if we aren't grain feeding cattle on an industrial scale we will have a lot fewer beef brugers. Less militant hardworking vegans will be highly respected - if only for the larger portions of Coq Au Cidre they leave the rest of us.
Finally, can I take this opportunity to volunteer for the first crew of the Urban 75 Tea Clipper? I'd suggest that having dropped off our supply of IPA in India and stocked up on tea and spices, we leave some room for a few mediterranean delicacies on the way back!
I wish it wasn't pie in the sky.

It sounds like a nice place to live to me.