The group is heading to Waterloo in Belgium to raise money for their regimental charity. They were seen off by David Cameron.
Boris and Jo Johnson share the family's trademark ultra competitiveness, but in many ways they are very different people.
Jo Johnson will head up the Policy Unit inside Downing Street in a shake-up to inject fresh Tory thinking into Government.
– David Cameron, speaking to The Sun
I want him to get back in Parliament. I think he's great. It's a bit like football - if you have got a great striker you want him on the pitch.
It's up to him. He can complete as Mayor, or he can stay on as Mayor and come back to the House. I want him on the team.
Following mounting speculation about Boris Johnson wanting to become prime minister David Cameron said:
– David Cameron, speaking to The Sun
It wouldn't be a great job to have if people didn't want it. There is nothing ignoble about wanting my job.
David Cameron has made a plea for Boris Johnson to return to Parliament and run in the next election. The Prime Minister said it is up to the Mayor of London whether he completes his term in City Hall, but wants him "on the team".
David Cameron was speaking in an interview with comedian James Corden, who was guest Editor of The Sun. Running in the next election is "what I think" Mr Johnson should do, Mr Cameron said.
The Prime Minister has unveiled a £15.5 million funding package to support innovative firms today, pledging to "make Britain the best place in the world in which to start and grow a business".
World-class technology experts will be given fast-tracked visas under a push to attract the best international talent to the United Kingdom's digital sector.
During a visit to Tech City, Britain's answer to Silicon Valley in East London today, Mr Cameron outlined plans for the Government to open up the exceptional talent visa route - usually reserved for international leaders in science and the arts - from April next year.
Between 2009 and 2012 the number of tech and digital companies in London increased by 76%, growing from 49,969 to 88,215.
27% of all job growth in London comes from the tech/digital sector, employing 582,000 people in London.
Mr Cameron has signed a book of condolence at South Africa House in London.
He wrote: "Your cause of fighting for freedom and against discrimination, your struggle for justice, your triumph against adversity - these things will inspire generations to come.
"And through all of this, your generosity, compassion and profound sense of forgiveness have given us all lessons to learn and live by."
He ended his message with a quote - "Blessed are the peacemakers for they shall be called the children of God."
He signed off with his name and "London Dec 6 2013".
It's emerged David Cameron has been following the exploits of a high-class escort agency on Twitter.
One of the Prime Minister's official accounts was linked to the Carltons of London's feed on the micro-blogging site, technology news website The Register found.
But Downing Street indicated that the agency may have first been followed under Gordon Brown's premiership.
The @Number10gov account is the official Twitter feed for the office of the Prime Minister and automatically followed anyone that chose to follow it until 2009 - while the former Labour leader was in power - when the practice was stopped.
This afternoon I’m meeting Vladimir Putin in No10 - we’ll hold a news conference before heading to the G8 in Northern Ireland
The Prime Minister was at the new London Gateway port in South Essex, where it was announced that Marks & Spencer will build a new distribution centre, creating 700 jobs.
Hundreds of workers will also be employed in construction of the centre, which is to due to open in 2016.
London Gateway, the UK's newest deep-sea container port, opens later this year.