No, this is not permissible. This army has fought almost all Muslim nations and colonized them! You must not be affiliated with them in any way.

Sheikh, I am a Young Muslim male who is currently contemplating on many career choices ,one of which is to be a british soldier.Is this within islamic boundaries? I wish not to compromise my religion in anyway. Sheikh, their is an imam by the name of Assim Hafiz who serves as a chaplain and he claims that they are not fighting islam Short defence available on youtube