There is no such thing as an average day at Brighton's PDSA PetAid hospital.

Staff normally treat about 90 sick or injured animals each day and these can range from an elderly tortoise with with an abscess to a cat hurt in a road accident.

Many will come under the experienced eye of senior veterinary surgeon Jonathan Gravestock.

One of his patients this week was Bonnie, who underwent an ultrasound scan to get an image of her internal organs.

She is one of hundreds of creatures great and small treated at the centre in Robertson Road, Preston Park, Brighton.

It provides a lifeline to thousands of pet owners in the city who cannot afford veterinary treatment but want to enjoy the benefits of owning a pet.

As it relies on donations, the charity decided to throw open the hospital doors and invite the public to see behind the scenes.

They were given guided tours of the consulting rooms and operating theatre and had the chance to meet some of the patients.

The People's Dispensary for Sick Animals was founded in 1917 by Maria Dickin who was shocked by the animal suffering she witnessed while visiting the poor in London's East End.

The charity has had a presence in Brighton since the first dispensary opened at 47b Portland Street in 1927.

PDSA hospitals opened in Upper Lewes Road, Brighton, in 1928, Montague Place in 1937 and Station Road, Portslade, in 1951.

The charity moved from Upper Lewes Road to 16 Oxford Street between 1932 and 1937. The site was re-developed in 1978 when the premises were enlarged and modernised.

Construction of a new purpose-built hospital started in August 1992 at Robertson Road and opened in May 1993.

In recent years the clinic has dealt with some unusual customers.

One was Wilbur, a 61- year-old tortoise, who was taken to the hospital where Mr Gravestock found an abscess, which was removed under general anaesthetic.

Wilbur stayed at the hospital for 12 days.

Another lucky recipient of treatment was plucky Pepe, a nine-year-old tortoiseshell cat who lost a leg and badly injured another in a road accident last year.

Owner Daran Harris rushed her to the PetAid hospital where she was stabilised with fluids and antibiotics, before being X-rayed.

She had suffered a broken right hind leg, seriously damaged her left hind leg and broke all her toes.

She also had severe skin loss and open wounds.

After a couple of days Pepe's left hind leg deteriorated, which meant she had to lose it.

During the operation, her broken right hind leg was also repaired with pins and wire. The surgery took two hours and afterwards Pepe had to stay in hospital for four days.

Thanks to Mr Gravestock and the staff, Pepe's life was saved.

Mr Gravestock said: "PDSA PetAid services are entirely dependent on public support through donations and legacies.

"This enables the charity to help those pet owners who often have nowhere else to turn when their pet becomes ill or injured."

Les Crawley, who was at Wednesday's open afternoon, is chair of the Brighton PDSA fund-raising group.

He and a group of volunteers spend the whole year raising money in any way they can for the hospital.

Mr Crawley said: "We have a band of very cherished volunteers but recruitment can be a problem.

"We would love younger people to get involved. The charity is not just an animal charity, it's a people one too.

"When you see an elderly lady go into the hospital with her old dog, often it's her only companion."

Mr Crawley, his wife Ranee, and volunteers including Jean Kettle, have helped raise more than £60,000 in seven years for the hospital, which treated 24,500 cases in Brighton last year.

Anyone who wants to volunteer to raise funds should telephone 01273 505770.

There is a PDSA PetAid hospital in 46 towns and cities in Britain.

Treatment is free to those who cannot afford private veterinary fees and who are in receipt of housing benefit or council tax benefit.