Help the Aged store manager, Nick Stokes, said: "We had a look in the bag and at first we thought it was a rubber snake."

Then the creature began to move, and slipped out of the bag and beneath a sorting table in the shop.

The RSPCA was called to capture the reptile, which was identified as an American corn snake.

Abandoned pet

Corn snakes are not poisonous, but Mr Stokes told BBC New Online that this was little consolation at the time.

"Snakes are snakes", he said.

The RSPCA said the pet snake would have been uncomfortably cold in the bag which had been left outside a house to be collected by the charity.

RSPCA spokesperson Sari Eldridge said: "It is a sad example of someone getting bored with their pet and dumping it."

She said the snake is available for adoption through the Southridge Animal Centre in Potters Bar.