To provide a streamlined process of obtaining volunteers for major incidents or events I suggest a national register of volunteers divided into categories dependant on requirements.
In relation to returners to services such as the Police in most instances when an officer retires an exit interview takes place with a check list provided by HR.
I suggest a tick box is included to ask if an individual would like to volunteer in the future for major events of national import. Employers could send these to a national register where the administration could carried out centrally.
The general public who did not go the employer route could go directly to the register to show their interest. Specialist skills held by individuals could be recorded there such as First Aid or if police checks or security vetting was valid with end dates.
The British population are known for their great desire to volunteer as with the 2012 Olympics. I suggest a national register so people know where to go would only help to increase the volunteer pool and reduce costs to the government by in effect getting free labour.