Up to 30,000 police officers might have come into contact with asbestos at training facilities, the Metropolitan Police have said.
The force confirmed it was examining a number of buildings used for firearms training between 1980 and 2007.
It also said it was in the process of contacting “a large number of officers” who might have been affected.
At one time asbestos was frequently used as a building material.
Exposure to asbestos can cause serious and potentially-fatal diseases including mesothelioma, lung cancer and asbestosis.
It is thought it is generally only people who regularly work directly with materials containing asbestos who are at any serious health risk but Health and Safety Executive figures estimate there are 5,000 deaths a year caused by exposure to the substance.
Short-term exposure is not considered to pose a danger.
The HSE says asbestos can be present in any building built or refurbished before 2000.
The Met said it would undertake rigorous examinations at all buildings where firearms training took place to establish whether asbestos was present.
Ch Supt Mike Gallagher said officers still working for the force had been contacted.
He said inquiries had identified a possible issue at some buildings used historically and detailed investigations had been carried out to identify all those individuals potentially affected.
“Due to the time period in question and number of possible sites, we need to make contact with a large number of officers,” he added.
“This will include those who have left, retired, or transferred, so clearly this is a process which will take some time.”
Professor John Cherrie, of Heriot-Watt University in Edinburgh, who has worked on several asbestos research projects, said most people were exposed to low levels of asbestos at some time during their life.
“However, people who become ill from asbestos are usually those who were exposed to it on a regular basis, most often in a job where they worked directly with asbestos-containing materials.”