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
The closures are part of wider measures designed to revive the group's fortunes in the wake of a disastrous 2014.
Craig Stevens is selling 85 figures and an extremely rare Boba Fett, the bounty hunter from The Empire Strikes Back, is the pick of the sale
Digby, who is just five weeks old and weighs less than 1lb, was found moments from death outside a block of flats.