The time, space and cost of design, parts acquisition, manufacturing, testing, advertising, shipping and customer service come out of that revenue.
Despite the richness of Welsh culture and the wisdom of the Welsh people, the capital and technical knowledge required probably exceed that of the average Welsh salaryman.
Subtract the VAT to get £20,833.
Then note the average annual salary for a man in Wales is £40,000. This would be a good income from a side project.