...Do you buy British with lower flower miles or help developing countries with their export potential? ...
Personally, I have a very rational and unsentimental view about sourcing produce.
From the point of view of helping the entire world, it is best if every country is able to do whatever it can, however little that is. So if some country is able to grow something, but can't do anything else, then they should be encouraged to do that, even if we could do it ourselves. We should be devoting our efforts to improving the sorts of things that we do best.
Many arguments about food miles are quite spurious. You burn more petrol driving to the supermarket than is used to transport the food you buy half-way round the world.
When you buy an apple in the shops, the cost of transportation is part of the price. You can buy apples grown in New Zealand for the same price as home grown. I just buy the cheapest. Just as New Zealand can send its apples to us, our growers should be exporting to New Zealand, during the months when apples are out of season there.