According to official figures the force has shelled out £1.24m on informants since 2015-16, making it one of the biggest spenders of any force in the country.
The biggest spend took place over the last 12 months, where informants were paid £272,931 by the force – an increase of more than a third on the previous year.
The data was provided by the force in response to a Freedom of Information request.
West Midlands Police said the services of informants was required to “prevent and detect crime and disorder” and that the authority to use them was “constantly reviewed in the context of necessity and proportionality”.
“The basis for this is when all other, less intrusive methods, have been used and/or considered and cannot be successfully used,” the force said in a statement.
“Effectively, a view might be taken that the use of [an informant] is only taken when all other methods of conventional policing have been considered.”
All payments to informants were “in line with national guidelines” and varied from year to year “dependent on investigations”, the statement added.
In its response to the FOI, West Midlands Police refused to confirm how much had been paid to informants relating to Black Lives Matter or environmental groups.
The force said only that it could neither “confirm nor deny” that such information was held.
Across the country 32 police forces spent around £18m on informants over the period, with the Met accounting for almost a third (£5.2m) of the total bill.
The national system for remuneration is classed as confidential.