The squirming larvae were first found to have curative properties during World War I.

Dr William Baer noticed that maggots were getting into the wounds of people injured on the battlefield.

Instead of making the wound worse, they helped clear it up.

Dr Baer starting using maggot therapy at Johns Hopkins Hospital in Baltimore - with excellent results.

But with the advent of antibiotics in the 1940s, the therapy went out of fashion.

However, according to the BBC's Trust Me I'm a Doctor programme, they are now making a comeback because of concerns about infections that are resistant to antibiotic treatment.

Breathing through their bottoms

Dr Stephen Thomas is the sole UK breeder of maggots.

He keeps flies in a sealed room and feeds them on pig's liver.

The flies lay their eggs on the liver. These are then separated and sterilised and develop into maggots.

The tiny maggots are sent out to hospitals in vials.

Maggots clean wounds by eating dead tissue. They first spit out enzymes that liquefy the tissue and then suck up like soup.

"They are very gregarious creatures and like to feed in close groups so they all get the benefits of the secretions they are producing."

Maggots are also able to breathe through their bottoms which means they can work very quickly because they do not have to keep coming up for air while they are feeding.

Bradford Royal Infirmary's leg ulcer unit is one hospital which uses maggot therapy.

'Better than surgeons'

Kath Vowden, a nurse at the hospital, says people think the maggots are going to be big fishing-type maggots.

But the ones used for treating wounds are very tiny.

Maggots are traditionally associated with death and fishing

They are put on the surface of the wound and then sealed in with a bandage.

The maggots only feed on the dead tissue.

Kath's husband Matthew Vowden is a vascular surgeon at the hospital.

He said: "Maggots are very small. They can be very exact about what they do. They can dissolve and digest dead tissue.

"A surgeon cannot be that exact and will harm some of the living tissue."

During the course of a three-day treatment, the maggots' bodies, full of dead tissue, expand from an average length of two milimetres to three times the size.

They leave wounds pink and healthy.

Mr Vowden says many doctors are still reluctant to use maggot therapy. He believes this is because they are not advertised like drugs are and because patients are put off by them.

"Patients expect tablets. They don't expect maggots," he said.