He was the Victorian geologist who discovered the existence of dinosaurs.

But despite being a pioneer of the prehistoric, the memory of Dr Gideon Mantell seems to have eroded.

A commemorative plaque in Brighton to mark the home where he lived for five years is today barely readable.

Weather and pollution have taken their toll, destroying the stone designed by Eric Gill in the Thirties.

It is an issue close to the heart of history enthusiast and Hove resident William McIlroy, who wants to see plaques around the city restored for the benefit of future generations.

Mr McIlroy said: "Many of these stones marking important moments in history have been destroyed.

"Hundreds of people walk past them every day without even knowing they are there.

"So many of these plaques have been made of the wrong materials or put in the wrong places. They need replacing."

Dr Mantell, a medical doctor as well as a geologist, was born in Lewes in 1790.

He found a huge fossilised tooth at a site near Cuckfield, identified as belonging to a 40ft long creature similar to an iguana.

Dr Mantell named it Iguanadon. It was the first time the concept of a dinosaur was considered.

He moved to 20 Old Steine in 1833 and opened a museum there.

Today most of the letters on the plaque on the outside of his former home have been rubbed away and the stone blends into the wall of the building, which now houses offices.

Along Marine Parade is another unreadable plaque. Herbert Spencer was a philosopher and scientist who lived and died at 5 Percival Terrace, Kemp Town.

Spencer, originally from Derby, is known for having developed principles of evolutionary biology before Darwin and is credited with creating the phrase "survival of the fittest".

On his death in 1903, the Brighton Gazette described him as one of the greatest thinkers of the Victorian era.

His stone plaque is so weather damaged it is impossible to read any of the details.

Mr McIlroy said: "It's a total eyesore. I happen to know it's there but people passing by would not."

Some plaques are not in such a bad state and just need a quick clean.

George Jacob Hoyoake, who started the co-operative society which became the Co-op, lived in Camelford Street, near Marine Parade, between 1881 and 1906. His plaque is slightly rusty but repairable.

Some, such as that for musician Ray Noble, are hidden. To access the plaque on the building at 1 Montpelier Terrace where Mr Noble was born in 1903 it is necessary to go into someone's private garden and climb nine steps.

Others are in mint condition, such as that for Lord Olivier, who lived at 4 Royal Court between 1961 and 1979.

Mr McIlroy said: "They are so important for local history.

"And when you look at it from the crudely commercial point of view, they attract people to the city."

A spokeswoman for Brighton and Hove City Council said: "We have no budget to repair and restore plaques.

"The only way we could do it in the near future would be with an injection of cash from somewhere."

l A campaign has been launched for a blue plaque to mark the spot where one of Brighton and Hove's first gay icons, Lord Alfred Douglas, better known as Bosie, lived.

Bosie is best known as the youth whose fling with Oscar Wilde led to the Victorian author's spell in Reading prison.

Supporters, led by Kemp Town web designer Adrian Cooper, want him recognised for his own literary contributions and are trying to raise £1,500 for an English Heritage-style blue plaque at his former home in St Ann's Court, Nizells Avenue, Hove.