A British department store has worked out a formula it says will make sure festive feasters are never again left holding the short end of a pulled cracker.

"Success is mainly down to the angle, grip, cracker size and 'lines of failure' or where the cracker is likely to tear," said Debenhams.

When pulled, a cracker will always rip at a weak point connecting the reinforced barrel section to the tails, the store added.

By pulling backwards and down at the same time, it is possible to concentrate the force across the top face of the opponent's line of likely failure.

The cracker should be gripped about an inch from the end of the tail closest to the barrel. The tail should be kept in line with the barrel as it is pulled backwards and downwards, with an even force.

For the serious puller, the store has worked out a mathematical formula: O = 11xC/L + 5xQ, where O is the optimum downward angle for pulling the cracker.

C stands for the circumference of the barrel, L is the barrel's length and Q is the quality of the cracker -- pricier versions are often made from stronger material which will increase the optimum angle of pull.

Q has a value of one, two or three depending on whether the cracker is cheap, standard or expensive.

Debenhams said the formula should produce a two-digit figure between 20 and 55 degrees, which is the optimum pulling angle below the horizontal.

"Don't worry, it's less complicated than it looks," it adds.