LOL, not sure why GR is getting all this criticism, so many places have dress codes, M* or not, and most are more extensive and more sternly announced than the message on the RGR website.
The Ritz Dress Code (throughout hotel and for eating sandwiches)
https://www.theritzlondon.com/faqs/
Veersswamy (M* Indian) DC: https://www.veeraswamy.com/faqs/
“Our dress code is Smart / Elegant.
No track bottoms, shorts (men), torn or scruffy jeans, flip flops or sportswear & baseball caps are allowed. Our restaurant managers will use utmost discretion and have complete authority to deny access to any guest whose attire and overall appearance doesn’t comply with these requirements.”
Rules (no stars, popular London restaurant)
“Dress code: Whilst Jacket or tie are not required, we prefer smart dress.
Rules is delighted to welcome Families during the day, however, Children under ten years of age will no longer be allowed in the Restaurant after 7.00pm.
NO SHORTS OR SPORTSWEAR.”
Groucho Club (private club for arts and media folk) :
“Do you have a dress code? We assume the effortless and impeccable good taste of our membership would not necessitate a code, however the notorious and exhaustive Groucho Book of rules states the following: 'The wearing of string vests is fully unacceptable and wholly proscribed by Club Rules.“
Fabric (night club)
“We operate a casual dress code so jeans, trainers and caps are allowed. If you'd like to check if a particular item of clothing is permitted, please call the office between 10am-7pm. And yes, you can wear shorts in the club. We DO NOT allow fancy dress, business suits, team colours, flags or any day glow wear.”
Sketch (M*)
very particular and a bit terrifying, ‘art smart’ ’with a sense of style’ specifies fabrics. (Nothing diaphanous or see through) No beachwear, nothing ‘immodest’, requires guests to be ‘well dressed at all times ‘ and will chick people out for not meeting their standards. I can’t copy the link.