He appears in the mission "Crew Expendable" in Call of Duty 4: Modern Warfare. Wallcroft, Griffen and Gaz dropped down to the ship to retrieve a bomb headed to the Middle East after 'Soap' MacTavish andJohn Price cleared the first wave of Russian troops. Wallcroft and Griffen were ordered to cover Price's back while the rest went into the ship. Before Price and the others could retrieve the entire bomb, Baseplate reported a MiG airstrike on the way. Wallcroft and Griffen fled to the safety of the evac chopper. Price requested an update on their status and they reported that they were already in the chopper but told the four to get out just as the MiG's opened fire. The four managed to escape the ship and the chopper brought the group back to London. Wallcroft is also randomly generated in the mission All In.
Wallcroft and Griffen reappear in the Call of Duty: Modern Warfare 3 campaign mission, "Mind the Gap", as SAS squad leader. After the SAS picked up some suspicious cargo, the contents were not yet known. Baseplate assigned Wallcroft, Griffen and Marcus Burns and other SAS to intercept a group of 5 trucks with one of the crates carrying the unknown cargo. Marcus, Griffen and Wallcroft intercepted one of the trucks that was still at the docks, but it didn't have the cargo so Wallcroft, Griffen and Burns went into the subway where another truck was suspected of holding the contents. After avoiding other trains and civilians whilst chasing the train with a truck, the leading truck's driver was shot and killed, which caused the truck to crash and derail the train. Wallcroft and Burns survived but Griffen and the other SAS soldiers were killed in the crash. Wallcroft and Burns battled their way through the subway station, eventually meeting up with local police outside. Wallcroft and Burns met up with other SAS and police who had blocked off another road where another truck was suspected to pass through. Indeed, one showed up and the men opened fire on the truck, killing the drivers. They secured the truck and tried to contact Baseplate for a report on the other trucks were but received no response. Unfortunately, another truck exploded near the Big Ben, killing a family, dozens of bystanders, and exposing the public to the deadly chemical. Wallcroft is later heard reporting that Downing Street is within the contamination radius.
At the start of "Crew Expendable", in the helicopter, Wallcroft is not present. Only Price, Gaz, Griffen, a randomly generated SAS soldier, and the two pilots can be seen. However, he will instantly spawn opposite where the randomly generated SAS soldier was sitting (between Griffen and Gaz), once Soap, Price and the SAS soldier have rappelled down.
Wallcroft is the announcer for the SAS in Call of Duty: Modern Warfare 3's multiplayer.
If the player chooses to "Skip the disturbing content" the decoy will explode but Wallcroft will continue standing unfazed in the explosion radius. This is interesting considering everyone else goes flying into the air as a result of the explosion.
He and Griffen have plot armor in Crew Expendable and Mind the Gap.
He is voiced by Craig Fairbrass, who also voiced Gaz and Ghost.
Wallcroft is the only character voiced by Craig Fairbrass who does not have a prominent role through an entire game.
He is also the only character that Craig Fairbrass voiced that hasn't been killed by an antagonist.
In the Call of Duty 4 level Crew Expendable, Wallcroft (or Griffen, as it is unknown who is speaking) is the first character to swear in the Modern Warfare series, and the first character in the entire Call of Duty series to swear overall.