Downing Street cats Larry and Palmerston have had their "most brutal fight yet" according to a political photographer who is urging Downing Street to "take responsibility" for the spats.

Fur flew as the two clashed yet again on Downing Street, according to Steve Back who said Larry lost a collar during the latest encounter with Palmerston, the Foreign Office's 'Chief Mouser'.

Mr Back runs the Twitter account Political Pictures, which has been documenting their fights.

Palmerston on the left braces for another onslaught credit: Steve Back 07884436717 photographer

He told The Telegraph: "It was utterly appalling, the fighting has been going on for weeks and weeks. This morning I was there covering normal political events and suddenly Palmerston appeared from the foreign office.

"Suddenly these two were at each other hammer and tongs. First they were hissing at each other and we didn't think they were going to fight, so we walked off.

"The next thing we heard there was this terrible screaming. we turned around and they were fighting outside number 11 literally ripping fur off each other. Palmerston's ear is in a terrible mess and Larry has lost his collar."

He continued: "I went and broke them up, and as I broke them up I got scratched on the leg. I was wearing long trousers but the claws went through to my skin.

Stealth moves: Palmerston launches an aerial assault credit: Steve Back

"They were really going at each other. They kind of split up, then disappeared under the photographer's ladders and started again. In the end they stopped, they were just exhausted."

The photographer has been watching them fight, and is worried that if no one takes action, their rivalry could end in death.

He said: "They are going to end up killing each other - they were brought in as a PR stunt and now it has gone too far.

"No one seems to care - it's happening outside Theresa May's window! There now even are rumours the Cabinet Office is going to get a cat - it's cat madness on Downing Street as they are all fighting over a small space."

Claws out: both Toms stick their claws in credit: Steve Back

Armed police had to break them up at one point, Mr Back claimed.

He added: "An armed policeman pulled them apart and got a huge cut on his hand. I wish someone would do something about it – it's gone too far."

Pictures of one fight show Palmerston has a clump of fur missing, and Larry had to have veterinary treatment for a sore paw, which was allegedly injured during a fight with Palmerston.

Meow - that hurt. credit: Steve Back

Battersea Dogs and Cats home have advised Westminster on how to deal with this "catty" behaviour after seeing the press coverage of the cat fights.

Battersea’s Head of Catteries, Lindsey Quinlan said: “Our Feline Welfare Specialist at Battersea Dogs & Cats Home 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.

“It’s not uncommon for felines to get catty with each other which is a normal part of predation, play and social conflict.

"Like the 3,000 cats that Battersea rehomes every year, both Larry and Palmerston have been neutered which reduces the risk of them attracting attention from other cats though 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 both be able to roam outside their Westminster homes in their designated areas without meeting each other whilst still being able to fulfil their important mousing duties.”

The two were both adopted from Battersea Dogs and Cats home; Larry in 2011 and Palmerston earlier this year.

They are soon to be joined by another male cat from Battersea - the Treasury recently adopted domestic shorthair Gladstone as their Chief Mouser.

He has yet to be let out on the street, but there has been speculation as to whether he will join the cat wars.

Political battle: The claws are out between Downing Street cats Larry and Palmerston credit: Steve Back

The turf war has sparked an online declaration of allegiance, with Twitter users choosing sides by selecting a #teamlarry or #teampalmerston hashtag.

Palmerston even trespassed in No. 10, sneaking round the door as it opened and darting into the Prime Minister's home.

He was unceremoniously evicted by police officers, and then took part in a defiant stand-off with one of them.