He has one job - to rid Downing Street of mice - but it appears Larry the cat is not up to the task, after he was caught on camera letting a rodent go.

Rather than hunting down the creatures Number 10 said in the past he prefers to take cat naps, but the latest incident confirms he may lack the killer instinct of many politicians who have lived there.

Photographer Steve Back, who captured the incident, said : “Larry the chief mouser of Number 10 came face to face with a tiny little mouse, which after some play time, got away safely”.

The 10-year-old tabby has his own Twitter account with more than 107,000 followers, making him more popular than many MPs.

His Twitter account explained his latest failure to deliver by saying he was playing a tactical game, before claiming he was "on a diet".

It said: “My friend @PoliticalPics thinks I look sleepy; I’m actually just lulling the mice into a false sense of security...”

Larry was recruited from Battersea dogs and cats home during the Cameron years to tackle the rampant mouse problem at the famous address

But after this latest incident,s some have accused of failing to deliver the results expected of him.

He is one of several Whitehall pets, including Evia and Ossie of the Cabinet Office and dogs Rex and Oscar, who live upstairs at Number 10.

Larry’s mousing skills are said to pale in comparison to those of his fellow moggies, Palmerston, who lives at the Foreign Office, and Gladstone, who minds the Treasury.