Using Natural Dyes in the UK

Farming the Dye Plants

All three of the plants to create the primary colours that can then be combined to create a full spectrum of colours can be grown in the UK. With the weld and madder plants being able to be grown on industrial or waste land. Utilizing land that is otherwise empty in a productive way.
Growing indigo could require more set-up however, this could be avoided if the indigo pigment is extracted from woad leaves.
All these plants could be grown and framed in the UK then used to dye textiles for British brands. Further research into what farming requirements and laws would have to be abided by to set up to grow these plants is needed.

Commercialisation 

There are some companies who are already using natural dyes on a large scale but they are still mostly smaller brands.
Botanical Inks - Botanical Inks is a natural dye house based in Bristol. They offer small and large scale dyeing of natural textiles using non-toxic natural dyes. Prioritizing the well-being of our environment and ourselves.
Damson Madder - Damson Madder is a clothing brand based in London who create slow design fashion. They have experimented with natural dyes for their products to create sustainable and responsible clothing.