I am not sure about Somerset but there is a place in Taunton, down the Weir, called Joe The Tailor.....their prices are usually very reasonable and it has been around for a very long time
Shay R. replied:
I had a dress tailored at Mr. and Mrs. K's Tailoring on County Street a few months ago. They did a really good job. https://www.yelp.com/biz/mr-and-mrs-k-custom-tailoring-somerset