British Prime Minister Boris Johnson has full confidence in his under-fire health secretary, his spokesman has said, despite private WhatsApp exchanges emerging in which he appears to slam the minister's "hopeless" handling of the pandemic, AFP reports.

The endorsement of the beleaguered Health Secretary Matt Hancock came hours after Johnson's messages with former chief aide Dominic Cummings — who stepped down from the role in December — were posted online by the controversial ex-advisor.

Cummings, who has spent recent months savaging both his former boss and Hancock, tweeted screenshots of the exchanges apparently between him and Johnson in March and April last year as Britain battled the first wave of the pandemic.