BORIS Johnson was back at work in Downing St just hours after his fiancée Carrie Symonds gave birth to a healthy baby boy but No 10 was reluctant to give many details about the birth.

Suspicions were raised that Ms Symonds, 32, had given birth prematurely since the previous expectation had been that the baby would arrive in early summer.

“I’m not going to go into the details of the birth,” declared the Prime Minister’s spokesman, who did mention Mr Johnson was present throughout the birth.

He was equally unforthcoming on which hospital was involved, other than saying it was an NHS hospital in London, what time the birth happened, what weight the baby was, if it was a medical emergency, a Caesarean birth and what number child this was for the PM.

Asked about the timing of the birth and whether it was premature, the spokesman insisted he would not go into any details other than relay the information already given.

Asked why he would not say which hospital was used when the public was told the hospital Mr Johnson was recovering in from the coronavirus, he said he had nothing more to say on this.

The spokesman repeatedly referred back to the official statement issued earlier by the couple’s spokeswoman, which read: "The Prime Minister and Ms Symonds are thrilled to announce the birth of a healthy baby boy at a London hospital earlier this morning. Both mother and baby are doing very well.

"The PM and Ms Symonds would like to thank the fantastic NHS maternity team."

The birth of his son marks another dramatic development in Mr Johnson’s personal journey during the past weeks and months.

Last July, he fought off challengers to become the Conservative Party leader and Prime Minister.

In the ensuing months he was engaged in a tumultuous parliamentary battle with opposition parties over Brexit but in December went to the country and won an 80-seat Commons majority.

By January, Britain had left the EU and entered a time-limited transition period as the Government sought to negotiate a trade deal with Brussels.

But within two months the country was in the grip of the coronavirus and in an unprecedented social lockdown. Two weeks later, Mr Johnson was in St Thomas’s Hospital and within 48 hours was in its intensive care unit, fighting for his life. He returned to his Downing St desk on Monday.

There was uncertainty yesterday morning about whether or not Mr Johnson would take PMQs today and Downing St remained coy about the prospect, raising suspicions he was not as well as he had hoped to be.

Asked if this reticence was because it was known then that Ms Symonds was about to give birth, the spokesman said: “I’m not going to get into any of that.”

He did confirm the PM was with his fiancée this morning for the birth and was “now back at work in No 10” and was expected to speak to Sir Keir Starmer, the Labour leader, this afternoon about the Government’s approach to the pandemic.

Asked if Ms Symonds was also back at No 10, he declined to comment.

However, the spokesman confirmed the couple did intend to continue living in Downing St, in the flat above No 11, and that Mr Johnson, 55, would be taking paternity leave but not just yet.

“I do expect the PM to take a short period of paternity leave later in the year rather than now,” he explained.

Asked which number child this was for Mr Johnson, the spokesman said: “The PM is delighted about the birth of his baby son and I’m not going to comment on his other children.”

However, in extending his good wishes during a business statement in the Commons, Jacob Rees-Mogg, the Commons Leader, congratulated the PM for joining "an exclusive club of members who are fathers of six". He added: “It is a huge joy for the whole country.”

Good wishes poured in after the birth was announced.

Mr Johnson’s father, Stanley, said he was "absolutely delighted" and "thrilled" by the birth of his grandson.

Nicola Sturgeon, the First Minister, declared: “Some good news - sending congratulations to Carrie and the PM. And wishing health and happiness to the wee one.”

Sir Lindsay Hoyle, the Commons Speaker, said: "On behalf of everyone in the House of Commons, may I say congratulations to the Prime Minister and Carrie Symonds on the birth of their son. Such happy news amid so much uncertainty – 2020 is certainly a year they will never forget. "

Labour leader Sir Keir Starmer tweeted: "Wonderful news. Many congratulations to Boris Johnson and Carrie Symonds."

Sir Ed Davey, the acting leader of the Liberal Democrats, said: "Many congratulations to the PM & Carrie Symonds on the birth of their son!"

The Archbishop of Canterbury, Justin Welby, tweeted: "Congratulations and prayers for @BorisJohnson and @CarrieSymonds as they welcome their son into the world. Wishing them every blessing and happiness."

From abroad, Shinzo Abe, the Japanese premier, said: "My dear friend, @BorisJohnson, warmest congratulations on the birth of a sweet baby boy!"

Scott Morrison, the Australian PM, tweeted: "Congratulations @BorisJohnson and Carrie on the birth of your baby boy. Nothing better than being a dad, an absolute blessing and even more so after the tough time you've had recently. Sending you and Carrie our best wishes from Australia."

Several Cabinet colleagues took to Twitter to add their congratulations.

Health Secretary Matt Hancock said: "So thrilled for Boris and Carrie. Wonderful to have a moment of unalloyed joy!"

Iain Duncan Smith, the former Tory Party leader, tweeted: "Congratulations @BorisJohnson & @carriesymonds such wonderful news! Baby boy!"

Chancellor Rishi Sunak said: "Great to hear Downing Street is getting a new resident. "Congratulations to @BorisJohnson and @carriesymonds on the birth of their son."

Sajid Javid, the former Chancellor, tweeted: "Congratulations @carriesymonds @BorisJohnson. Such wonderful uplifting news!"