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.

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.