The BBFC has confirmed that it has granted Activision's upcoming Call of Duty: Modern Warfare 2 an 18 certificate – making it in the first in the series to receive the highest age restriction.
All previous titles in the series have been rated at either BBFC 15 or PEGI 18+. And considering the gratuitous flesh-burning and execution scenes seen in the last game, World at War, the violence level in the new title must be quite extreme.
There isn't much in the way of information in the BBFC's ruling, though it notes that the game contains around 40 minutes of cut scenes. The rating was arrived at based on 45 minutes of in-game footage.
UPDATE: The BBFC has contacted MCV to point out that it does playtest the games it rates. The 45 minutes of gameplay footage mentioned is supplementary. It also stated that further details about exactly why the game was rated 18 will be published on its website on November 1st.