And they were. Intense competition from telephone bidders led the buyer, the New York collector, dealer and market-influencer Jose Mugrabi to pay £371,250, or about $415,000, for the piece. It was a new auction high for the artist and more than six times the Christie’s estimate of £40,000 to £60,000.

Dealers have lengthy waiting lists of buyers seeking work by the hottest names, so when these works appear on the auction market, they can fetch far more than gallery price tags.

At Art Basel this year, for example, Pilar Corrias, Ms. Self’s London gallerist, said she sold a new work for less than $100,000. Such gulfs between “primary” and “secondary” market prices inevitably encourage speculation.

“I am trying to keep a level head in regard to the auction prices,” Ms. Self said in an email Thursday. “I do not personally base the value of my work on these results.” Ms. Self is currently an artist-in-residence at the Studio Museum in Harlem and recently designed a limited-edition handbag for Louis Vuitton.

London hosts three series of high-end contemporary auctions each year. But the continuing uncertainties surrounding Brexit have made collectors reluctant to consign trophy works here, particularly in the summer. Christie’s held no evening contemporary auctions in London for two years before returning this June.

Sourcing top-quality material remains a problem, dealers say. “It’s very mixed. Not a strong sale. You wouldn’t come back from holiday for this,” Ivor Braka, a private dealer and collector based in London, said of the 32 works up for auction at Christie’s Tuesday.