This suggests that there are more than 100million "mystery keys" in the country, weighing more than 1,000 tons.
The poll, by Esure insurance, found that the average woman owned 10 keys but didn't know what two of them did.
Men own an average of eight, but again the purpose of two of these is unknown.
The research also found that, while the average bunch comprises nine keys, more than a quarter of those polled owned between 10 and 15 different keys, with a further nine per cent of people possessing 21 or more separate keys.
The poll also found that one in five homes had a key hidden within 10 feet of the front door, with the most common hiding place a garden rock, followed by plant pots and door mats.
One in 10 respondents did not bother to change locks after losing a set of keys, and two thirds left a set of keys with neighbours, family or friends.
The over–55s are the most trusting, and frequently leave keys with others, while a third of under–25s said they had never done so.