London Ambulance Service's (LAS) 999 operators have had to take calls down on paper due to a computer problem.
In the past few weeks the computer-controlled call-taking system has crashed.
It means staff have had to take calls by hand and then pass information to paramedics by radio, instead of the computer doing it automatically.
An LAS spokesman said the problem had now been corrected and patients' lives had not been put at risk.
During busy periods, some 999 calls have been diverted to the Metropolitan Police control room.
The problem, caused by a software upgrade in July, has been compounded by staff shortages in the LAS control room
The LAS spokesman said using pen and paper to take call details was a "tried-and-tested" system and one previously used by the service before the computer system was introduced years ago.
He said: "Although we are currently nearly at full control room staffing, we have also been experiencing some difficulties in fully covering some shifts during August and this has put additional pressure on our ability to manage periods of particularly high demand.
"As a result, there have been a limited number of occasions when incoming calls have been diverted to the police for a very short period.
"This arrangement is part of our normal contingency planning and as such is always in place to deal with surges in 999 calls.
"It should be noted that despite all these issues, the service is meeting its key performance target of getting to 75% of all life-threatened patients within eight minutes."