Although prostitution isn't illegal in the U.K. Brothels are
I can hardly see plod or local authorities wasting their time to visit a brothel just to see if the girls are naked in reception or not 
They do do routine inspections looking for signs of trafficked girls / coercion etc, this was a girl at Sandys before it got shut down, anyway an AI overview -
Women in UK brothels often wear clothes in reception to maintain a professional appearance, respect the privacy of other clients, and comply with safety or management rules designed to avoid public indecency accusations. Wearing clothes also helps with initial screenings, managing business, and providing a level of comfort or modesty.
Sandwell Council
Sandwell Council
Safety and Professionalism: According to safety advice, wearing clothing initially allows for assessing clients, managing personal safety, and ensuring a professional, "business-like" atmosphere before any intimate interaction occurs.
Discretion and Legal Considerations: In the UK, keeping a brothel is illegal. Maintaining a "discreet" appearance in the reception area helps prevent drawing unwanted attention, as visible nudity or overtly provocative behavior in public-facing or semi-public areas could lead to complaints or legal issues.
Client Comfort: The reception area is a waiting area. Allowing clients to enter a controlled environment where the staff are appropriately dressed for a business transaction provides a more comfortable experience.
"Business Attire": Similar to other industries, some establishments may enforce a policy requiring staff to look presentable in a reception area.
Sandwell Council
Sandwell Council
The focus in the reception area is on professional interaction, while the private rooms are where the services are performed