UK is not a unitary state. Scotland, Wales and Northern Ireland have devolved parliaments
Correction:
The UK is a unitary state, because all sovereignty ultimately rests with the UK Parliament in Westminster. The devolved legislatures in Scotland, Wales, and Northern Ireland exercise powers granted to them by Westminster, and those powers can in principle be altered or revoked by it.
That’s how devolution works in a unitary state: power is devolved from the center. Denmark and Greenland are a similar example. By contrast, in a federal system like Germany, the Länder (states) are the original source of sovereignty, and the federal government’s powers derive from them.