False, recurring pro-Kremlin narrative on the decaying Western countries.
In his report published in November 2018, Special Rapporteur Philip Alston does identify poverty as a distinct concern for the United Kingdom. The 24-page document, however, contains no reference - let alone a comparison - to sub-Saharan Africa, where more than a quarter of the population faces starvation at any given moment.
RT's fabrication might be based on the following remarks, cited by The New York Times: “When you think of the special rapporteurs on extreme poverty and human rights, you expect them to be visiting sub-Saharan Africa or Haiti. You don’t expect them to be visiting the U.K.”
The comment does not compare poverty in the UK and elsewhere, it predates the UN report, and it was not made by Philip Alston, but by an expert from the University of Bristol.