Just outside London is a large boarding kennels, which three councils also use as a dog pound. Lost, stray and abandoned dogs are sent to pounds such as this all over the UK, where they are kept for just seven days. Then, if no one claims them, or rescues can't offer a space, they are put down – almost 9,000 of them last year, according to the Dogs Trust.

The pounds vary, but this one is the kennel of your nightmares: outdoors, no heating, damp stone pens, metal cage doors, scarcely any bedding, or human contact, no walks, horrendous noise – barking, yelping, whining. I have never seen such petrified, miserable and freaked-out dogs. The strays have seven days of this purgatory, then, if the rescues are full and there's nowhere to put them, it's curtains.

Rescue centres may not put healthy dogs down, but council pounds have to. I'm at this one with Jane, who works for a small dog-rescue charity in North London, to collect three dogs. One, a staffie, is trembling in its plastic bed, too scared to move. The second dog, a small terrier, bites Jane and the third barks non-stop. Half an hour later, once they're at the rescue kennels, there's some warmth, peace and quiet at last, and two kind women, who calm them down and bring out a soft white duvet for the terrified dog. Just a few minutes of affection and comfort, and the terrified staffie is transformed, from shivering wreck, to trusting dog, lying on his back having his tummy stroked. I managed not to blub in the pound kennels, but this finishes me off.

"Every time I go there I get upset," says Jane. "They're there because people don't want them any more, because they're old, ill, deaf, incontinent, have cataracts, or just bad teeth, or lumps and bumps, which might be cancer, but owners can't afford the tests, or don't want to pay for them, never mind the treatment. We can sort out the health problems, but not dog- or person-aggression. We haven't the facilities. It's so sad." And it's going to get sadder. More people are skint, and dogs are expensive.

Rescue centres, chock-full already, are now bracing themselves for March and the deluge, when everyone who's sick of the darling puppy or dog they bought for Christmas chucks it out.

The Dogs Trust has been saying "a dog is for life, not just for Christmas" for 35 years, so they're starting a new campaign, presspaws.org.uk, to try to make people think before they buy one. I wish them luck, and they'll need it, because it's easier than ever to buy a dog now – online, in markets, and pet shops, from some boy in the street. Over 50,000 a year come flooding in from battery-style puppy farms, usually even nastier than this dog-pound, but still allowed and often licensed by councils. Blame these and other greedy and irresponsible breeders, not the vets, wardens and rescuers who have to deal with the grim mess. How many thousand dogs will spend their last seven days in the pounds this year?