A policeman stabbed outside a railway station is the latest example of an "epidemic" of "senseless acts of violence" against officers, a senior official has said.
Just hours after the attack on Friday, another man in his 20s was stabbed in the Dalston area in the early hours of Saturday morning, and died of his injuries.
The British Transport Police (BTP) officer in the first attack was fortunate that colleagues were nearby to restrain his attacker, BTP Federation chairman Nigel Goodband said.
- Read more: Sadiq Khan announces £13m funding to tackle serious youth violence
- Read more: Home Secretary calls for ‘more leadership all round’ to stop children being drawn into crime
"I wouldn't like to have imagined what could have happened if those colleagues weren't in close proximity", he said.
The force said the officer was approached by the suspect and attacked with a knife outside Ilford Station, east London, at around 9.45pm on Friday night.
He was taken to hospital for treatment and discharged on Saturday to recover at his home.
A man has been arrested over the incident, BTP said.
Mr Goodband told the Press Association: "I'm told it was totally unprovoked.
"It's shocking - knife crime and the wider epidemic of attacking police officers is a real concern to us all.
"We're witnessing this too often now, it seems certain elements of society see it as acceptable to attack police officers.
"We are now seeing senseless acts of violence against those who are there to protect society."
Witnesses described seeing the bloodied officer outside the station as it was put on "complete lockdown".
Counter-terrorism police are not involved at this stage, it is understood.
'Hotbed for drug dealers'
Watch: Former detective Mick Neville tells Julia Hartley-Brewer stop and search is a 'useful tool'
One woman, who lives in the area and wished to remain anonymous, said officers on horseback had been patrolling outside the station over the past week and described the area as a hotbed for drug dealers.
Meanwhile, a murder investigation was launched over the Saturday morning stabbing.
- Read more: 'What's worse: a policeman's hands in your pockets or a knife stuck in your belly?' says former Scotland Yard detective
Emergency services were called to Kingsland Road in Hackney at around 6.30am, but despite the efforts of medical staff, the victim died in hospital several hours later.
No arrests have been made and a crime scene with road closures remain in place, Scotland Yard said.
The killing takes the total number of homicides in the capital so far this year to 121.