British Prime Minister Boris Johnson and fiancee Carrie Symonds have named their son in tribute to their grandfathers and the doctors who treated Mr Johnson for COVID-19.

Ms Symonds, 32, posted a picture of her cradling the newborn on Instagram, saying she “couldn’t be happier”.

“Introducing Wilfred Lawrie Nicholas Johnson born on 29.04.20 at 9am,” she posted on Saturday.

“Wilfred after Boris’ grandfather, Lawrie after my grandfather, Nicholas after Dr Nick Price and Dr Nick Hart – the two doctors that saved Boris’ life last month.

“Thank you so, so much to the incredible NHS maternity team at UCLH that looked after us so well. I couldn’t be happier. My heart is full.”

The two doctors are experts in infectious diseases and ventilation, and shared their “warm congratulations” with the couple.

“We are honoured and humbled to have been recognised in this way, and we give our thanks to the incredible team of professionals who we work with at Guy’s at St Thomas’ (Hospital) and who ensure every patient receives the best care,” they said in a statement.

“We wish the new family every health and happiness.”

PM Boris Johnson and partner Carrie Symonds have welcomed their first child together. Photo: Instagram

Ms Symonds and Wilfred are understood to be back in Number 10 Downing Street with Mr Johnson after the birth on Wednesday.

Just weeks ago Mr Johnson was discharged from intensive care where he had been battling coronavirus.

Ms Symonds also suffered symptoms of the disease.

Mr Johnson, who is currently grappling with the UK’s coronavirus crisis, is expected to take a “short period” of paternity leave later in the year.

The new family plans to live in their Downing Street flat along with their dog Dilyn, Mr Johnson’s office has said.

Wilfred is Ms Symonds’ first child, while Mr Johnson is known to have fathered five others.

-AAP