A London Ambulance Service spokesperson said:
“We carried out planned testing of our call answering system overnight but due to a technical issue we have been unable to switch back the system as normal, and are currently recording and allocating calls manually.
“Our staff are trained to operate the 999 system manually and we are continuing to prioritise our response to patients with a life threatening condition using the same assessment process as usual.
“Engineers are looking into this and will resolve the issue as soon as possible.”
More top news
Concern is growing for the welfare of a 28-year-old woman who has not been seen for more than two weeks.
A police officer in today's London Pride parade surprised his partner by proposing in the middle of the parade.
Record crowds are at this year's Pride in London parade as people show their support for the LGBT community after the Orlando shooting