A dog that mauled a puppy to death in front of its terrified owner has killed before, it has emerged.

Esther Shortt , of Allerton Road, Borehamwood, was left horrified when the Staffordshire bull terrier bit into her Cavalier King Charles spaniel ‘Ruby’ on a walk through Oak Hill Park, East Barnet, on Tuesday morning.

The 47-year-old fought to get the large mutt, which was not on a lead, off her beloved puppy but the injuries inflicted were so severe that the six-month-old had to be put down by a vet a short time later.

It has since emerged that the same dog killed another puppy in similar circumstances at the Church Hill Road park in November.

Police are powerless to take action because there is currently no legislation for police to deal with dog-on-dog incidents.

Grandmother-of-two Mrs Shortt stopped to read a text message on Tuesday in the middle of the walk when she heard Ruby squeal.

The personal trainer said: “It was like a nightmare. He had her in his mouth and wouldn’t let go. People ran over to help but we could do nothing. I was worried it would attack me – I was fearful for my life.”

When the aggressive canine eventually let go of little Ruby, he had inflicted fatal wounds and left Mrs Shortt in a state of shock.

She said: “I tried to ring my husband but I couldn’t speak. You just feel like you have let your dog down so much – I was totally helpless. Nothing would have stopped that dog.”

Mrs Shortt has been unable to return to the area to walk her other dog, German Shepherd ‘Lady’, and has cancelled fitness classes she runs in the park because of the trauma.

The Staffie’s owner, a man called Dale, regularly walks the brindle-coloured mutt in the park and once chillingly joked that his dog “could have Ruby for breakfast” as the puppy was so small.

He apologised to Mrs Shortt and swapped contact details in the aftermath of the horrifying ordeal.

He has reportedly been left devastated by the latest attack.

Mrs Shortt added: “He’s a nice man really but there’s no way that dog should have been off the lead.”

Theresa Sands’ puppy Bertie was killed by the same dog in chillingly similar circumstances on November 15, also at 6.30am.

Hearing Mrs Shortt’s story has brought back horrifying memories of her own experience and the retired council administrator has been left in a state of depression for the past few days.

The 64-year-old said: “It is just unbelievable. I’m sure the police told him to keep the dog on a leash after my attack but he obviously hasn’t. I blame the owner, not the dog.

“I remember thinking at the time I had to report it as it could happen again. But now it has.”

Police are looking into the latest incident but are yet to confirm whether any action is taken.

New legislation giving police powers to deal with owners whose pets attack other animals is expected to come in early next year.

Mrs Shortt said: “There needs to be a law to stop this. People can’t bring their dogs into the park out of fear. He’s ruling the park with his dog.”