There is absolutely a Constitution in the UK, it is simply not codified into a single document.

https://en.wikipedia.org/wiki/Constitution_of_the_United_Kin...

More importantly, the UK is a Constitutional Monarchy, with ultimate legislative power vested in Parliament rather than the Monarch.

You are technically correct. But the distinction between devolution and a Federation of states gets very blurry when you take a look at what's happening with voting in the US these days.

You are technically incorrect about the UK not having a constitution. It's just not all compiled into a single written document.