Former commander in the Metropolitan Police
Fifteen years ago, following discussions between all the emergency services, the Police service launched the 'gold' - 'silver' - 'bronze' system for all major policing operations.
It is particularly suited to those that require close co-operation between the police, fire and ambulance services, such as a terrorist bombing, or a train crash and is, like all good ideas, extremely simple.
With a gold alert, a police superintendent or above, sets the broad strategy.
It is then his or her responsibility to define the objectives - the 'what do we want to achieve?' issues.
The buck stops with the gold leader, who will operate from the main control room monitoring what is going on because it may be necessary to adjust the plan as things develop.
The silver commander takes the strategy and comes up with a plan to implement it. He or she has to sort out the 'on the ground' tactics and looks after the 'how are we going to do it?' questions.
He also looks to the gold leader to provide him with all the personnel and equipment that he needs to do the job.
There can be any number of bronzes. They are usually Inspectors or Chief Inspectors in charge of between 20 to 100 officers.
They are the people who deliver on the ground. They do what is required to achieve success.
On many occasions, sitting in the main control as gold, running a major incident such as a terrorist outrage, or a train crash, I not only had to oversee the event but also take on broader responsibilities.
It was my job, in order to ensure that there were no blockages in the system, to set up a co-ordinating group of all the top people involved, plus others whose expertise might be useful.
David Gilbertson was gold commander at the Southall rail crash
Depending on the incident, this might include Network Rail or experts in chemicals or biological hazards.
Government departments and local authorities might need to be represented. The security services might want to be involved.
You need to be a diplomat on occasions because there are times when any or all of those mentioned are more concerned about the preservation of reputations, than the job in hand. I always tried to keep focussed.
Being gold for any big operation is challenging and is not a job for the faint-hearted.
Job well done
I had to watch events in real time and take decisions that could, quite literally, mean life, death or serious injury for the people under my command or those that we were dealing with.
I wasn't out there, 'in the muck and bullets' - but my responsibility was wider and deeper.
My predecessors from previous generations no doubt thought that they were doing a grand job by being on the scene, but they could only see what was around them.
Sitting in the control room, with a bank of 20 to 30 CCTV screens in front of me and five channels of radio being monitored, I knew what was happening across an entire city and had to react accordingly.
At the end of a long day, (up to 15 hours is not unusual), I would often leave the control room with a sense of a job well done.