PBS’s “Masterpiece,” the enduring Sunday night British drama and mystery franchise, will expand by at least 20 hours next year, an approximate 50 percent increase, with the new hours being broadcast either before or after the program’s traditional time slot of 9 p.m. Eastern time.  The new hours start on Jan. 18, when the six-part mystery “Granchester” will be broadcast after new episodes of “Downton Abbey.” “Wolf Hall,” adapted from two Hilary Mantel novels, follows in April, with other imports later in the year. They come with exclusive corporate sponsorship from Viking River Cruises, and are a result of the booming interest in the genre by United States viewers.  Led by “Downton Abbey,” the audience for “Masterpiece” has more than doubled since 2010. In 2014, new episodes of “Masterpiece,” through September, are drawing an average 6.4 million viewers weekly; for the same period in 2010, new episodes averaged 2.8 million viewers, “Masterpiece” said.  “How often does this happen to a television series that’s 43 years old, to grow, to be expanded?” said Rebecca Eaton, the program’s executive producer.  The expansion and the additional corporate support, which “Masterpiece” would not quantify, underscore just how much the program’s fortunes have improved. After the longtime sponsor ExxonMobil ended its $9 million in annual support in 2004, “Masterpiece,” which is presented on PBS by the Boston station WGBH, had only a handful of intermittent short-term corporate sponsors until 2011.  Ms. Eaton pointed to the program’s 2007 freshening up of its look and rebranding — it was originally known as “Masterpiece Theater”— as the start of its turnaround. Then, she said “lightning struck twice,” in “Sherlock,” whose first season was broadcast in 2010, and the first season of “Downton Abbey” in 2011. The success of those two programs “has created a gusher of programming coming from our U.K. partners,” Ms. Eaton said.  In the last two years, PBS has broadcast some British dramas on Sunday nights adjacent to “Masterpiece,” but the programs, including “Call the Midwife,” have not fallen under the “Masterpiece” brand.  “When ‘Masterpiece’ was able to step up with some sponsorship from Viking River Cruises and a desire to own some of the additional space, we were happy to partner with them,” said Beth Hoppe, PBS’s chief programming executive. The British drama audience is loyal, she said, “and was clamoring for more.”  Viking River Cruises has sponsored “Masterpiece” since 2011, and Ralph Lauren came on board in 2012. That arrangement will continue for the 9 p.m. broadcasts.  Richard Marnell, senior vice president for marketing at Viking River Cruises, said the company tracked the viewing habits of its travelers closely and they appreciate the “Masterpiece” sponsorship. “Our awareness as a company has gone up dramatically, and ‘Masterpiece’ is the most-cited individual program that has created that awareness in our target demographic,” he said.  In addition, Mr. Marnell said, the company has tracked a “noticeable increase in web traffic” because of “Masterpiece.” Those factors went into the decision to become the sole sponsor of the added broadcasts, he said, adding that when “Masterpiece” approached the company, “We immediately said yes.”  A version of this article appears in print on November 3, 2014, on page B3 of the New York edition with the headline: ‘Masterpiece’ Franchise on PBS Is Adding Broadcasts . Order Reprints|Today's Paper|Subscribe
“Masterpiece,” the 43-year-old English drama franchise, is capitalizing on the runaway success of “Downton Abbey” by adding new shows and more airtime early next year.