Professional emergency services are summoned immediately by

An authorized person is somebody who has thetask of carrying out a specific job. Anybody may call the emergency services if they are needed.
The four emergency services are: Police Fire Ambulance Coastguard.

All are called by dialling 999 on an outside-line telephone. The emergency services operator will ask you which service you require. In certain cases the police will automatically be called,for instance in the case of a severe fire.
All emergency telephone calls are recorded on tape at the telephone exchange. You will be asked for your name,the place where the emergency is and where you are calling from. With the introduc- tion of electronic telephone exchanges the number which you are calling from is automatically recorded,and you will be asked for the number to help confirm that your call is not a hoax.
Many companies have a direct telephone line to the fire station,and these automatically call the fire service if a fire is detected by sensors or by break- ing the glass of a fire alarm. In such cases,if the fire service is called out and there is not a fire,they may charge the company a large fee. So,do not tamper with such a device unless you are authorized to do so or there is a dangerous fire.