The BBC's Robert Pigott visits recent cruelty cases at RSPCA Harmsworth Hospital

The Royal Society for the Prevention of Cruelty to Animals says it continued to see an increase last year in the number of animals found abused and living in appalling conditions.

Convictions for cruelty in England and Wales rose by 17.5%, a figure the animal welfare organisation calls "alarming".

It says the rise is partly the result of more efficient co-operation with the public, but that cruelty is growing.

And it says the people who committed some of the worst crimes could not be traced, because the animals had not been fitted with microchips.

The RSPCA's Chief Officer of Inspectorate Tony Crittenden said: "Such unsolved cases clearly show the need for animals to be microchipped, so that pets are permanently linked to their owners.

"That way, unscrupulous owners who commit such cruel and barbaric acts of violence could be traced and brought to justice.

"I would love to see every animal in the country microchipped. The Utopian situation would be to make it a legal requirement.

The BBC's Margaret Gilmore: "The RSPCA's national helpline received on average a telephone call every 20 seconds last year"

"Our inspectors work tirelessly to prevent cruelty but they continue to see an increase in the number of animals found abused and living in appalling conditions."

The RSPCA's Communications Director John Rolls said the charity was currently discussing the introduction of compulsory microchipping with the Department of Trade and Industry.

The chip, similar to a grain of rice in size, is inserted just under an animal's skin by a vet.

He said: "I believe that the establishment of the link between the owner and the animal would encourage people to think about actually taking animals on."

Injured tail

Cases dealt with by the RSPCA included a three-foot iguana found abandoned in a field of sheep in Somerset.

The end of the reptile's tail was missing, and she had abscesses on her tail, head and chest.

The iguana, a native of South America, was nursed back to health at an RSPCA centre.

Another case, this time in Sussex, involved a farm where an RSPCA inspector found 50 dead sheep, along with some too diseased to survive.

The farmer, who was involved in a wedding celebration when the inspector called, told the court he had been unwell and caring for his elderly mother.

He was fined, but not banned from keeping animals.

In the Leicestershire town of Loughborough the body of a Rottweiler cross-breed was found hanging from a bridge in September last year.

The body was too decomposed to allow vets to establish the exact cause of death.

An RSPCA inspector called it "the worst case of animal cruelty" he had seen during nine years at Loughborough.

The RSPCA singles out several other cases:

• a cat that was scalded and had ribs and a leg fractured
• three greyhound puppies which were left to starve and which survived by eating their dead siblings
• a dog thrown from a car.