STORY: "Last week when fresh allegations arose, the Prime Minister did not immediately recall the conversation in late 2019 about the incident," Ellis told parliament of former deputy chief whip Pincher, who resigned over his conduct last week.
Johnson has come under pressure from accusations that he lied about what he knew when he appointed Pincher to a role involved in offering pastoral care in the Conservative Party.
Johnson is already facing growing frustration among his governing Conservative Party over what some say is a scandal-ridden administration, with some lawmakers trying to renew attempts to unseat him.
Facing off with Ellis in parliament, Labour opposition deputy leader Angela Rayner said there was an "ethical vacuum" in Johnson's government.
The prime minister was "either negligent or complicit" in his handling of the allegations against Pincher, she said.