Just weeks ago the Jack Russell was facing almost certain death, abandoned by dog traders who thought that a misaligned jaw would mean that he would never find a home.

But now the puppy is about to take up residence in one of the most famous addresses in the world as it is adopted by Boris Johnson and Carrie Symonds and moves into Downing Street.

The 15-week-old dog was rescued by Eileen Jones, who runs Friends of Animals Wales, after an anonymous tip off that he had an undershot jaw and was being abandoned.

Ms Jones said that after 14 years rescuing animals she often gets calls about ex-breeding dogs or puppies that are at risk and goes to meet the tipsters in lay-bys to rescue the animals.

Her volunteer run charity specialises in taking in sick dogs and arranges for them to be fostered before a permanent home can be found.

It thought that if the puppy had not been rescued it would have been shot.

Ms Jones, 66, is expecting to deliver the as-yet-unnamed Jack Russell on Monday long with one of her volunteer co-ordinators and the person who has been fostering him until now.

Plans for the adoption have been in place for weeks and the puppy has been living in a foster home with a cat to get it ready to move in with the notoriously territorial Chief Mouser.

But Mr Johnson and Miss Symonds will not escape the normal checks which every person adopting a dog has to go through.

Ms Jones has already visited Number 10 for a Pup Aid garden party last year but will be carrying out home checks today and will ensure “everything is being done in the same way as every other adoption”.

Ms Jones said: “He has been living with a cat for a few weeks and from my understanding there are a lot of things in place for training. He is only a baby so he is going to be very workable and he is a delightful little pup.

“I think he will settle in well although there may be more issues on the side of the cat, but as long as the puppy learns who is boss – which will be the cat – then everything will be fine.”

Mr Johnson’s suggestion of getting a dog at Downing Street was said to have been welcomed enthusiastically by staff, some of whom are said to have offered to help with walks.

Prime Minister Boris Johnson, with his partner Carrie Symonds, hosting a reception at 10 Downing Street. credit: PA

Unlike Larry, who is a permanent resident at Number 10, the puppy will belong to Miss Symonds and Mr Johnson.

The couple are said to have chosen the dog to highlight strict new anti-puppy farming legislation which comes into force in April.

Named Lucy's Law after a Cavalier King Charles Spaniel which died after being was rescued from a puppy farm, it bans the sale of kittens and puppies from third parties, meaning buyers must deal with breeders directly.

Marc Abrahams, the TV vet who has led the campaign for Lucy’s Law and who put Miss Symonds in touch with the Ms Jones, said that the was “overwhelmed” that the couple had chosen to drawn attention to the work of smaller volunteer-led charities.

“Lucy’s Law is now being highlighted by the Prime Minister and that is being seen by the world and hopefully they will take notice,” he said.

“There are so many boxes being ticked here and this is like a dream come true for us grass roots campaigners.

“They have saved a life and it will save so many others as it will open people’s minds to the possibility of taking in a rescue dog.”

The Government passed the legislation in May and Wales has since followed suit, with pressure on for Scotland to introduce similar restrictions on puppy farming.

It will make breeders more accountable and Ms Jones said that her volunteer run organisation has already seen an increase in dogs being abandoned as puppy farmers know that they will not be able to sell them on.