Labour's deputy leader Tom Watson will be quizzed by a group of MPs on 21 October over his involvement in the Leon Brittan abuse case. The MP raised rape allegations against the late former home secretary in a letter to Alison Saunders, the director of public prosecutions.

Brittan died in January without knowing the police had dropped the case against him and now the Home Affairs Committee, chaired by Labour's Keith Vaz, wants to probe Watson and senior officers from the Metropolitan Police about their conduct.

"The committee firmly believes that the Independent Inquiry into Child Sexual Abuse, which the home secretary has established under the chairmanship of Judge Lowell Goddard, is the most appropriate channel for these very important matters to be examined," Vaz said.

"Our evidence session is therefore intended as a continuation of the regular series of very helpful regular updates which the committee received from the Metropolitan Police in the last parliament and to hear evidence on a particular case. The committee fully appreciates that ongoing operational activities are a matter for the police and these areas will not be discussed during the session."

Watson has so far refused to apologise over his involvement, despite Prime Minister David Cameron urging him to make the move. "When anyone is accused of multiple sexual crimes – by numerous, completely unrelated sources – the police have a duty to investigate no matter who it is," the MP said.

The evidence session featuring Watson will start at 3.15pm BST and it can be viewed on Parliament TV.