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Downing Street and the Foreign Office have been advised to keep their cats inside after a vicious row over territory this morning.

Larry, number 10’s chief mouser, and Palmerston of the Foreign Office violently clashed on Downing Street as bystanders were forced to separate them.

Experts from Battersea Dogs and Cats home have now warned officials to keep the cats inside to avoid further fighting.

Battersea’s head of Catteries, Lindsey Quinland, said: “Our feline welfare specialist has been in contact with the teams in Westminster to advise them regarding Larry and Palmerston’s behaviour.

“These cats were chosen to be chief mousers to 10 Downing Street and the Foreign & Commonwealth Office based on their sociable, bold and confident nature.

“The only downside to these behaviour traits is that aggression can sometimes occur when the territories of two cats overlap.”

A photographer who separated the two felines claimed both cats were limping after their latest fight.

Larry has also received treatment for an injured right paw after battling with Palmerston over territory.

The photographer expressed concern that their battle may turn fatal if it continues to escalate.

Although Larry and Palmerston have both been neutered, their battle shows no signs of ending, and could escalate further after the Treasury introduced their new cat, Gladstone.

Ms Quinlan added that it would be a good idea to keep both cats indoors to avoid further violence.

She said: “It may be advisable that Larry and Palmerston have temporary restrictions on their outside access to reduce the risk of them meeting in their early days; there is plenty of space for more than one cat on the block in Westminster.

“They should be able to roam outside their Westminster homes in their designated areas without meeting each other while still being able to fulfil their important duties.”