Palmerston was overweight - AP

Palmerston, the Foreign Office cat, has returned to work after six months recovering from stress caused by civil servants constantly picking him up and overfeeding him.

Those working in the department have been warned not to touch the cat unless approached, and to stop feeding him treats.

In July, the cat was taken to the house of Sir Simon McDonald's Private Secretary in order to recover from stress; the mouser was overweight and had groomed all of the hair off his front legs.

Sir Simon, a senior civil servant, is in charge of Palmerston's well-being and on Monday morning issued a strict letter to staff, warning them that if they do not change their behaviour towards the cat, he may be retired for good.

Mystery has surrounded Palmerston's extended break, with some worrying the cat was gravely unwell and close to death.

However, these rumours were unfounded and the animal is happy and back to full health.

The letter reads: "He is happy, healthy and full of energy. His pelt is glossy and mostly grown back (over grooming is, I’m told, a similar habit to human’s nail-biting; the habit can take a while to kick). His diet is regulated and free of Dreamies. We need now to keep him that way!"

I am happy to announce that I will be returning to my Chief Mouser duties at the @foreignoffice this week! New guidance - the Palmerston Protocols - will govern my care in the FCO to make sure it’s working for me. (1/4) pic.twitter.com/j2AFKI0DGN — Palmerston (@DiploMog) December 2, 2019

Staff have been given four rules now the cat is back. Sir Simon wrote: "First, no-one (apart from his carers) should feed Palmerston. No Dreamies. No bowls of food under the desk for if he happens to drop by. Nothing!

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"Second, everyone must help keep Palmerston in the 'Palmerston Zone'. Cats are territorial. They fret when their territory is bigger than they can manage. They can cope with an ever smaller territory as they age. Palmerston has been king of King Charles Street, roaming from basement to fourth floor (with quad, Downing Street and occasionally St James’s Park thrown in) for nearly four years. We think he’s about six years old, ie entering feline middle age.

"With the vet’s help we have mapped a more manageable territory: the offices and area surrounding the Grand Staircase. Heavy doors mark the limits, now with (discreet) stickers proclaiming, 'You are entering/leaving the Palmerston Zone'. Please respect the Zone and return Palmerston if you find him straying further afield. Bear in mind that he loves to sit beside the door and dart through, if given half a chance.

"Third, everyone must respect Palmerston’s personal space. Allow Palmerston to choose whether he wants to interact with you: offer your hand as if you were introducing yourself to a stranger, and allow Palmerston to make the first move. Don’t wake him if he is sleeping. He has full choice and control of who he deigns to greet or imperiously ignores.

"Fourth, my staff office will serve as both my Outer Office and as Palmerston’s refuge: Palmerston HQ. If he is in Palmerston HQ, he is not to be disturbed. Palmerston is a friendly, outgoing cat, but we all need our privacy. Like Greta Garbo, sometimes he wants to be alone."