Sir Christopher was pictured covered in blood in a hospital bed and his wife, Baroness Meyer, told The Times she was “absolutely shocked by the brutality”.
The assault took place on Wednesday as the ex-diplomat was getting on the Tube and he was admitted to hospital in Paddington, west London, the paper reported.
A London Ambulance Service spokeswoman told The Independent that while it sent paramedics to Victoria station following the assault, they were cancelled en route and did not treat Sir Christopher or take him to hospital.
The British Transport Police said it had arrested two teenagers on suspicion of grievous bodily harm.
A spokeswoman said: “Officers were called to Victoria Station at 2.45pm yesterday, after receiving reports that a man had been seriously assaulted.
“A 16-year-old boy from Hillingdon and a 15-year-old girl from Croydon were both arrested on suspicion of assault occasioning grievous bodily harm.
“They have been released under investigation while enquiries into the incident continue.
“A man in his 70s was taken to hospital, though his injuries are not believed to be life-threatening or -changing.”
He later headed the Press Complaints Commission.
The brutal attack came just a day before US president Donald Trump was due to visit the UK.
But Britain “should care” about what the Republican president thinks when he arrives, the former ambassador said, adding: “Forget the woolly, sentimentalised rhetoric of the ‘special relationship’, we are talking hard national interests here.
“The plain truth is that the US is our single most important partner and ally and President Trump is its democratically elected leader.”