Turnbull & Asser has a long and distinguished history as a shirtmaker to his HRM Prince Charles and others. In the last few years, upon the death of the Prince's longtime tailor, he apparently began having his suits made by Turnbull & Asser. I looked at a few articles that commented upon the switch at the time - none seemed to clarify whether the Prince had gone with the ready-to-wear offerings or full bespoke, although I would assume it was bespoke. Regardless, the Prince's suitings were most likely made by Chester Barrie, at the company's clothing factory in Crewe.
Interestingly, at the time of Prince Charles' switch to Turnbull & Asser, it was reported that Chester Barrie was making some 30,000 handmade suits per year (1998), with the help of some 475 tailors. On top of that, the company was producing 117,000 machine-made suits, ultimately selling some $16 million in clothing for Ralph Lauren's Purple Label (while only managing about $5.5 million in clothing sales via their own Chester Barrie label).
I recently came across a double breasted blazer from Chester Barrie for Turnbull & Asser. With the readily-apparent level of handwork, its easy to see why the Prince went with Chester Barrie and Turnbull & Asser.