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.
And that's absolutely not what the commenter up-thread meant.
I find it weird that people would downvote this, I know you should not complain about it, but this comment is correct. The UK does have a (uncodified) constitution. Also of note; even countries with a codified constitution have parts that are uncodified.
From your link: "This enables the constitution to be easily changed as no provisions are formally entrenched."
It doesn't look like a duck, it doesn't quack like a duck, yet you insist that this goose-shaped creature is a duck.