The BBFC have cleared Metal Gear Solid 4: Guns of the Patriots for release in the UK, giving it a 15 rating. They cited that the game contains "strong violence," and went on to describe other details of the game, and why it got the 15 rating.
If you are sensitive to spoilers you might want to skip the following paragraphs.
In MGS4 "the player takes on the role of an aging soldier, Snake who can be armed with knives, guns and grenades," comments the BBFC. "During battles enemy soldiers die with small puffs of blood.
The weaponry includes petrol bombs, however there is no detailed portrayal of injuries. During cut scenes slightly more detailed violence is portrayed, such as enemy creatures spearing friendly soldiers and one protracted fist fight."
The go on "Violence may be strong but may not dwell on the infliction of pain or injury. It is possible for the player to progress stealthily through the game, avoiding violent confrontations where possible. The game also features one use of strong language and references to suicide and an implied child rape."