The 999 emergency call system - the first of its kind in the world - celebrates its 75th anniversary tomorrow.
The service was launched in London on June 30, 1937, following the deaths of five women in a fire at the home of a surgeon in the city in November 1935.
Glasgow became the second city to have the service in 1938 and it was extended to all major towns and cities by 1948.
The number of 999 calls has increased from more than a thousand in the first week of the service in 1937 to an average of 597,000 calls a week across the UK.
The early hours of New Year's Day is traditionally the busiest time, when up to 13,500 calls can be received each hour.
BT's managing director of customer service, Warren Buckley, said: "The 999 service is known for its reliability and professionalism. It's not only the world's oldest emergency call service having clocked up 75 years of experience in providing the UK with a communications lifeline in times of need, it's also one of the world's most respected and admired services.
"Our 999 operators are the first port of call for people seeking help and we're very proud of the part they have played in this essential service for the past seven and a half decades."
BT said around half of the 85,000 calls received each day by its operators in the UK were not requests for help, but were mostly made by children playing or customers accidentally dialling 999 or the European emergency number 112 from a mobile phone in a pocket or handbag.
Of the calls that are passed to the emergency services, 52% go to the police, 41% to the ambulance service, 6% to the fire and rescue service and 1% to the coastguard and cave and mountain rescue services.