Boris Johnson has condemned grime artist Wiley's "abhorrent" social media posts and urged Twitter to go fast to remove hateful content.
The Prime Minister's spokesman said the social media giant's response to a series of antisemitic posts by Wiley was "not good enough".
However Mr Johnson is not taking part in the 48-hour Twitter boycott by some activists, celebrities and MPs over its handling of his posts.
Wiley has been temporarily suspended from Twitter and Instagram over a series of posts, where he referenced antisemitic tropes and conspiracy theories, including comparing Jewish people to the Klu Klux Klan.
Priti Patel, the Home Secretary, wrote to Twitter and Instagram on Sunday to demand answers over why the offensive comments were left up for 12 hours.
Downing Street said Mr Johnson shared her view that the posts were "abhorrent".
The PM's spokesman said: "Social media companies need to go much further and faster in removing hateful content such as this."
"The message is clear: Twitter needs to do better on this," the spokesman added.
But Mr Johnson is not joining a boycott of Twitter because of the need to communicate "important public health messages", his spokesman said.
The PM posted a video on Monday morning about the Government's new anti-obesity drive, where he spoke about his own struggles to lose weight.
"But at the same time we have set out very clearly that Twitter's performance has not been good enough in response to the antisemitic comments made by Wiley and it needs to do much better," his spokesman added.
Britain's Chief Rabbi Ephraim Mirvis accused the tech giants of lacking "responsible leadership" over the furore.
In letters sent to Twitter boss Jack Dorsey and Facebook chief executive Mark Zuckerberg - whose company owns Instagram - Rabbi Mirvis said: "This cannot be allowed to stand.
"Your inaction amounts to complicity."
High-profile Twitter users announced support for the boycott using the hashtag #NoSafeSpaceForJewHate, including Lord Sugar, consumer champion Martin Lewis, TV presenter Rachel Riley and comedian Shappi Khorsandi.
Shadow Foreign Secretary Lisa Nandy also declared she would take part but Labour's official account said it could not take part as it needed to hold the government to account.
