Larry was the first cat to hold the appointment since stalwart ratter Humphrey was retired in 1997.
Humphrey was succeeded for a short period by Sybil, the pet of then Chancellor of the Exchequer Alistair Darling, in 2007 - but the renowned mouser failed to settle and returned to Scotland.
The Foreign Office appointed Palmerston, a moggy, in April to keep pests in Whitehall at bay.
An unofficial Twitter account set up under Larry's name posted today: "Does anyone know a good cat groomer available tomorrow? I need to make a good impression on someone ..."
It had earlier tweeted: "One final thing before they'll let you have the job @TheresaMay2016 - tell the people you'll keep me in Number 10."
- PA, AAP