Boris Johnson and Carrie Symonds’ new son is the latest baby to be born to a serving prime minister.

Downing Street has been home to a number of babies, with Tony Blair and David Cameron both adding to their families while in Number 10.

But that is a relatively recent trend, with a gap of more than a century before Leo Blair became a Downing Street baby.

Cherie Blair gave birth to Leo three years after Labour’s 1997 general election win.

Mr Blair’s youngest son was the first child legitimately born to a serving prime minister for more than 150 years.

In Cherie’s memoirs, Speaking For Myself, the QC revealed Leo was conceived during a visit to Balmoral, the Queen’s residence in Scotland.

Leo was born at Chelsea and Westminster Hospital in London on May 20, 2000 at 00.25am, weighing 6lbs 12oz.

He joined sister Kathryn and brothers Euan and Nicky in the Blair sibling ranks.

Before Mr Blair, it was Lord John Russell and wife Lady Russell who produced the last child to be born to the office holder of First Lord of the Treasury – the prime minister’s official title.

Lady Russell gave birth to two sons, George and Francis, during her husband’s first stint in office between 1846 and 1852.

After a century-and-a-half delay between prime ministerial babies, Downing Street only had to wait 10 years for the patter of tiny feet to return to its corridors.

Mr Cameron and his wife Samantha welcomed daughter Florence Rose Endellion Cameron into the world in 2010.

Mr Cameron had only formed a coalition government with the Liberal Democrats three months prior to her being born, with the general election that year producing a hung parliament.

Florence was delivered by Caesarean section at the Royal Cornwall Hospital in Truro while the Camerons were on their summer holiday.

She was Mr and Mrs Cameron’s fourth child, although their eldest son Ivan, who suffered from cerebral palsy and severe epilepsy, died the year before sister Florence’s arrival.

While promoting his memoirs, For The Record, last year, Mr Cameron said Florence, who was only five when the family left Downing Street in 2016, was hazy about his time in power.

He told the Cheltenham Literature Festival that his daughter had asked him: “Daddy, is it true, were you actually the prime minister?”