For his daily suits. He changed from Anderson & Sheppard bespoke for Turnbull & Asser MTM.Weren't some forum members saying that the prince abandoned bespoke tailoring in favor of MTM from T&A?
He still use Gieves for navy and military uniforms. G&H made his wedding suit in 1981; the suits for William and Harry at his wedding in 2005. Prince Charles may have used G&H for his wedding suit in 2005.
William and Harry use G&H themselves.
G&H hold all three British Royal Warrants: The Queen, Prince Phillip (Queen's husband) and Prince Charles.
So even if the royal family get a big discount at G&H and John Lobb, they spend serious amounts of money there. Prince Charles used Anderson & Sheppard for 20 years, he probably more then 20 suits from them, then think of spare blazers and trousers.