Bookdepository.com have up to 40% off a selection of best sellers including Sally Rooney's, 2020 Booker Prize nominees and some classics. Offer until 31st August. Deals are at their website.
You can also get 8.25% cashback (new customers) via Topcashback.co.uk/book-depository/
You need to click through to Bookdepository via that link to qualify.