Previous research has shown these rare pooches, known as gifted word learners (GWL), have a unique ability to learn the names of hundreds of different objects.

However, a new study, published in the journal Biology Letters, now suggests they can remember the names of some of these toys for an extended period.

The hope is that the talented dogs could help scientists understand more about how animals other than humans retain their memories.

Dr Claudia Fugazza, the head of the research group at Eotvos Lorand University in Hungary, said: "We know that dogs can remember events for at least 24 hours and odours for up to one year but this is the first study showing that some talented dogs can remember words for at least two years.

"The findings of our current study cannot be generalised to other dogs because we only tested GWL dogs, individuals that show a special talent for acquiring object words."

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The research is part of a project known as the Genius Dog Challenge and the scientists are urging owners who believe their dogs know multiple toy names to contact them via the project's website.