London Emergency Services Liaison Panel

The London Emergency Services Liaison Panel (LESLP) consists of representatives from the following agencies:
Established in 1973, the group meets regularly and is chaired by the Metropolitan Police Service. The role of the LESLP is to establish the correct procedures for a collaborative approach to responding to major incidents within London. A major incident could be anything from a terrorist attack to a natural disaster. 
A revised version of the LESLP Major Incident Procedure Manual (2019 edition) is published on the London Prepared webpages.
Major incident.
A "major incident" is defined by LESLP as "an event or situation with a range of serious consequences which requires special arrangements to be implemented by one or more emergency responder agency."
Definition of a "major incident" explanatory notes:
This definition is different to the definition of an "Emergency", a related term defined in the Civil Contingencies Act 2004.
An example of the declaration of a major incident is the emergency system activated during the 7 July 2005 attacks on London.
Declaration of a major incident.
Declaring a ’major incident’ triggers a response from each emergency service and other responder agencies. It takes time for operational structures, resources and protocols to be put in place. Declaring that a major incident is in progress as soon as possible means these arrangements can be put in place as quickly as possible.
A major incident may be declared by one or more emergency responder agency if any of the major incident criteria is satisfied. A major incident declaration will normally be declared by one of the emergency services. In certain circumstances, for example flooding, a local authority or other responder agency may declare a major incident.
It is important that all individuals who could be first on scene for their respective responder agency are able to declare a major incident, and that they understand the implications of declaring one.
A major incident declared by one emergency responder agency may not be so for another, however, each agency will attend with an appropriate response and notify relevant support organisations. This is so even if they are to be employed in a standby capacity and not directly involved in the incident.
Stages.
Major incidents are considered to have four stages, namely:
Co-ordinating groups.
In the event of a major incident, the formation of Strategic, Tactical and Operational co-ordinating groups (also known as Gold and Silver co-ordinating groups) will occur. These groups will be responsible for actions and co-ordination within their own spheres of activity.
References.
The London Emergency Services Liaison Panel (LESLP) Major Incident Procedure Manual conforms to the Joint Emergency Services Interoperability Principles (JESIP) 'Joint Doctrine: The Interoperability Framework, Edition Two, 2016'.