When the cover is kept on a leash, your wallet will still be stretched at the vet

Animal insurance is the fastest-growing market in the industry. But with all the caveats, is it worth the premiums?

You might be prepared to pay £4,000 for orthopaedic surgery and hydrotherapy to return your own joints to full working order, but would you cough up the same amount for your dog?

Thanks to spiralling vets' fees, pet cover has become the fastest-growing form of insurance in the UK.

Although it is marketed as giving animal lovers peace of mind, many policies actually provide inadequate levels of cover, according to research from Sainsbury's Bank, which provides pet policies.

Often, pet insurance is kept firmly on the leash, it reports: only 60 per cent of policies provide cover for vet fees in excess of £3,500.

And half do not give financial protection against long-term conditions and illnesses; in many cases, the costs of treatment for a recurring tumour would not be met after 12 months.

A lot of policies are riddled with such terms and conditions, as well as other exclusions, according to a survey by Which?, the consumer organisation.

"Pet insurance won't pay for any routine vaccinations - which insurers normally insist are kept up to date - neutering or routine care such as teeth cleaning," says a Which? spokesperson. "This means it doesn't cover the most common reasons for visiting the vet."

A rough industry estimate suggests that it costs between £50 and £500 a year to insure a dog, and £30 to £200 to cover a cat, so over the life of your pet, you should expect to pay out up to £5,000.

But given that most of our trips to the vet are the result of requirements that won't be covered, what do we get for our money?

Basic policies foot the bill for vet fees of at least £500 (see the table above) and pay out when your pet dies.

On the other hand, comprehensive cover of £200 compensates you for the following: a pet "counsellor"; a lump sum for cancelling a holiday if your pet should need life-saving emergency treatment; and liability for third-party damage.

Policies should cover your pet in the event of an accident or illness, and usually, the full cost of treatment, including surgery and drugs.

Developments in animal care mean the cost of treatment can be steep: mending a dog's torn ligament can cost £1,500, and an MRI scan will set you back some £1,000. A cat that has been hit by a car might need treatment costing £600.

As a rule, start insurance when your pet is young; a new policy for an older pet is generally more expensive. Most insurers will specify a minimum age that the pet needs to be at the start of the policy (normally eight weeks old), and you can keep the cover in place over the course of its life.

Starting insurance for a pet over eight or nine years old is difficult but not impossible. More Than has no age limit, but Churchill and Direct Line both stipulate a maximum limit of eight years old.

"With both vets and industry data showing that pets are living longer, it's unacceptable for insurers to only cover young pets," argues David Pitt of More Than.

"Veterinary care has developed significantly over the past decade, but as pets get older, they are more likely to suffer illnesses, which can often be lengthy and expensive to treat."

Cover won't stop as the pet gets older, says Peter Gerrard of the price-comparison website insure-supermarket.com - "it just becomes much harder to start a policy".

Wary consumers should check whether their insurer imposes limits on compensation. Some put a cap on a payout per ongoing illness, whereas others limit the overall annual payout. In either case, if a pet has a pre-existing medical condition, it is unlikely to be covered.

Some providers will also lower premiums for pets that have been electronically tagged.

Don't forget, you'll normally have to pay an excess with a claim, usually between £50 and £100.