This is, at best, a naive portrayal of how London and Washington start wars.
See the infamous Downing Street Memo [1].
In Washington, which often leads the rest of the West in military adventurism, Congress hasn't approved a military operation since 2002, despite a US-led coalition destroying sovereign Libya in 2011 and occupying Northern Syria since 2015.
Indeed, the 2002 AUMF authorized by Congress for the Iraq War is still in effect 20 years later [2], and used by the executive branch to dictate any military operation, bypassing Congressional approval.
[1] - https://en.wikipedia.org/wiki/Downing_Street_memo
[2] - https://en.wikipedia.org/wiki/Authorization_for_Use_of_Milit...