Wood Green, The Animals Charity and TotallyMoney.com have launched the Cost of Christmas Pets calculator to help prospective pet owners understand the total lifetime financial commitment involved with owning an animal.

According to the calculator, the most expensive animal is - by virtue of its longevity - the tortoise (£27,787 over 75 years), followed by a small dog (£19,224 over 15 years), a large dog (£17,234 over 11.5 years) and a medium-sized dog (£16,828 over 11.5 years). A cat comes in at £12,322 over 16 years. A chicken will set you back £4,701 (it's not clear whether they've offset the money you'll save in eggs). The cheapest is a fish, at £914.