They are purchased, but depending on what course you do, you are unlikely to need to buy as many textbooks in the UK as is expected in the US. In some cases, you can do an entire UK degree without needing to buy a single textbook.
I studied Physics in the UK, but spent one year of the degree studying abroad in the US. In the entire 3 years I was studying in the UK, I bought a total of 2 textbooks, both of which were purchased in the first semester - one general 'University Physics' book and one Quantum Mechanics textbook (I took approximately 25-30 classes in total over the 3 years, but didn't need to buy any other textbooks - I could if I wanted to, but it wasn't required).
In the 1 year I was in the US, I had to buy 8-10 textbooks (at least 1 per class, and it was essentially required that you buy them).