A senior police officer was sent indecent images and an indecent video of child sexual abuse but failed to report it because of a serious error of judgment, a jury has heard.

Supt Novlett Robyn Williams was sent the “disgusting” video by her sister via the messaging service WhatsApp. Williams, 54, is on trial for possessing the indecent video and failing in her duty to report it. The high-ranking Metropolitan police officer denies the charges.

The Old Bailey heard that Williams’s sister, Jennifer Hodge, was first sent the video by her partner and then passed it on to 17 people on WhatsApp in February 2018.

One of those was Williams, who was accused by the prosecutor, Richard Wright QC, of failing in her duty to report it immediately: “Why do we say in particular, it was her obligation to report the video and deal with it? Because Miss Williams is a serving police officer of high rank.”

Wright added: “We say that the defendant, Williams, failed to act because she knew to do so would place her sister and her sister’s partner at risk of arrest and criminal investigation.

“We do not suggest that these defendants had any sexual interest in this video, nor do we say that they were distributing it or possessing it for any sinister purpose. This is instead a case in which we allege that each of them made serious errors of judgment about how to handle this video and in dealing with it as they did, each of them has committed serious criminal offences.”

The image in question was a video of a girl aged five or six being sexually abused by a man and lasted just under one minute.

“As an experienced officer of high standing, we say she knew full well what was expected of her and moreover that there was an urgent child welfare need to report the video as soon as she saw it,” Wright said.

Williams did not do so, the crown said. It is also alleged that she was aware of its nature from a tile or thumbnail that would have been clearly visible to her.

Records from WhatsApp showed that Hodge sent the message just before 11am on Saturday 3 February 2018 to 17 people including Williams. Then Hodge sent a message expressing her outrage about the video: “Sorry had to send this it’s so sad that this person would put this out please post this and let’s hope he gets life.”

The crown say that 40 minutes later, before midday on the Saturday, Williams opened WhatsApp. Wright said: “She would have seen a tile [thumbnail] that showed the first frame of the video. It would have been clear … and we say it would have been immediately obvious exactly what it was: an indecent video of a child.”

The jury heard Williams then tried to contact her sister, calling and texting. Hodge later sent a WhatsApp message to Williams asking: “Could you find out if it’s been reported?”, which the prosecutor said was a reference to the indecent video.

Williams and Hodge later spoke but Wright told the jury the senior officer still did not report the video.

Another person sent the video by Hodge reported it to police. A police investigation began, which identified Williams as one of those who received the video.

The trial continues.