ACCOLC – Access Overload Control

ACCOLC (Access Overload Control) is a British procedure for restricting mobile phone usage in the event of a major emergency. It is similar to the GTPS (Government Telephone Preference Scheme) used for landline phones.

This allows the mobile phone networks to restrict access to a specified area to pre-registered mobile phone numbers only. ACCOLC will usually be requested by the Police Incident Commander but the request can also come from the Cabinet Office.

The system is designed to restrict civilian access to the mobile network during an emergency when it is important that lines are kept free for priority emergency service personnel.

Mobile phones work on a cell by cell basis, these towers are spread all over the country and your phone will pick up the nearest available cell or mast and use that to make the call. Once the ACCOLC has been invoked the network will find the cells in the area of the emergency and begin to run the system on those masts.

Those phones that have been registered with the networks will be allowed access to those cells while people who haven’t will receive a fast beep (called a Fast Busy Signal), if the user receives a recorded message saying lines are busy or a normal engaged tone then this will indicate that ACCOLC is not being used.

While this can be a frustration or a nuisance to normal mobile phone users it is often a necessary and important process for regaining control during an emergency situation.

It’s worth noting that not all callers are barred from making calls in an area where ACCOLC is in operation, if the call is made to an emergency service number (112, 999) it will go through as normal.

The Access Overload Control was activated when officers of the City Of London Police spoke to managers at O2 plc, this was during the early stages of the 7 July bombings in London at Aldgate tube station. This limited the calls in the area to those police staff that had their sim card details registered for this priority access.

It is also reported that the BBC and other Broadcasters had reporters who had numbers registered with the service as part of their public-service remit in keeping the people of the UK informed about what was going on.

During the 7 July bombings the police decided not to shut down the entire network, however many people thought it was, as they were unable to make calls in the first hours of the terrorist attacks, as stated above those people would have heard a recorded message or a normal engaged tone.