LONDON — The number of people who said they were sexually assaulted by Jimmy Savile, one of Britain’s most popular television hosts, expanded to 300 from 200 in just the past week, and other people may have acted with him, the Scotland Yard officer heading the investigation said Thursday.

The officer, Cmdr. Peter Spindler, described Savile, who died in October 2011 at 84, as “undoubtedly” one of the most prolific sex offenders in recent British history, during a 50-year career as a self-styled pied piper for the young, the sick and the lonely. Spindler said that in preliminary telephone interviews with 130 of the potential victims, 114 of them had accused Savile of criminal behavior ranging from “inappropriate touching” to rape.

Of the 300 complainants, he said, all but two have been women.

Spindler said the “vast majority” of the accusations logged by the police were against Savile alone, with the remainder involving Savile and others or episodes in which the entertainer was not implicated. Although the commander specified that investigators had found no evidence of a “pedophile ring,” as some published accounts in Britain have suggested, he said that a number of “living people” were under investigation.

Spindler said his investigation, code-named Operation Yewtree, had not yet led to any arrests, but he implied that they might not be far off when he said that the police were preparing “an arrest strategy.” In the meantime, he said, police investigators were proceeding cautiously with Savile’s accusers, spending as much as four hours on each initial interview.

Spindler spoke at a news conference and in interviews with British news organizations. The weight of the evidence against Savile, he said, is overwhelming, not least because of the similarities in what the accusers have told the team of officers — raised to 30 in recent days, from an original group of 10 — about the abuses.

“We have to believe what they are saying, because they are saying the same thing independently,” he said.

The BBC reported Wednesday that Savile, a bachelor, was investigated but never prosecuted for sexual abuse at least half a dozen times during his television career.