Gladstone (born c. December 2014) is a British cat who is the resident chief mouser to HM Treasury in Whitehall, London.

He is a black domestic short-haired cat, who, at eighteen months old, assumed the position of chief mouser in late June 2016.

The decision to introduce an official mouser was taken by John Kingman, former acting Permanent Secretary at the Treasury.

[8] Food for Gladstone is taken care of by Treasury staff, who volunteer the modest sums required for his daily needs.

[14][15] He often receives trinkets such as cat toys, Christmas baubles from Brazil,[16] a personalised collar, and a Halloween handmade knitted scarf from Australia.

In March 2017, Gladstone was featured in the London Time Out magazine's 'Pet Power List: definitive guide to the political animals of Westminster'.