The MP5A5 is a 9mm submachine gun, designed by Heckler & Koch. It is suited to CQC situations, when over penetration needs to be avoided, and where a compact fully-automatic weapon is required.
Flynn had an MP5A5 in his helicopter. When he met with Tammy and Andy at Wembley Stadium, he aimed it at them when demanding to know where Doyle was. He lowered it when he discovered Andy and Tammy were the only survivors.