I don't think they entertain negotiation/haggling. The price is the price...
"A haggle-free experience
All our cars are competitively and transparently priced and we don’t add on any hidden admin fees. We offer our best price upfront, saving you the hassle of having to haggle."
Yup, download from the Lexus website
https://www.lexus.co.uk/owners/about-my-lexus/manuals/#hero
While you're there sign up to My Lexus (top right of page) and input car details for service history etc, etc..