In August 2018, Ethical Consumer searched WH Smith's website, www.WHSmith.co.uk, and found that the company sold a number of products containing leather.
Leather, as the hide of a dead animal, naturally decomposes. To prevent this decomposition the leather industry uses a cocktail of harmful chemicals including trivalent chromium sulphate, sodium sulphide, sodium sulfhydrate, arsenic and cyanide to preserve it. Tannery effluent also contains large amounts of other pollutants, such as protein, hair, salt, lime sludge and acids. These can all pollute the land, air, and water supply making it a highly polluting industry. As a result the company lost half a mark in the pollution and toxics category.
In addition, as leather is a slaughterhouse by-product, the company lost half a mark in the animal rights category.

Reference:

https://www.whsmith.co.uk/ (16 August 2018)