An amateur palaeontologist has unearthed the biggest dinosaur to be discovered in the British Isles - and possibly Europe - from a cliff overlooking an Isle of Wight beach.

Scientists who have just finished analysing the dinosaur's two neck bones believe it grew to about 66 feet long and weighed up to 50 tons. It lived around 130 million years ago when Britain was subtropical and still connected to Europe and North America.

Gavin Leng, a local fossil hunter, first unearthed one of the dinosaur's neck vertebrae in 1992, but its true importance was recognised only after it was cleaned and prepared by scientists at the University of Portsmouth.

Darren Naish, a palaeontologist at Portsmouth, said that one of the fossilised vertebrae, which is more than two feet long, indicates that the creature belonged to a group of long-necked dinosaurs called the sauropods.

"I can't think of anything that is as near as big as this one. The size makes it one of the biggest sauropods in Europe - in fact at the moment it is the biggest so far reported scientifically," Mr Naish said.

Features of the vetebrae indicate that the dinosaur was closely related to two other well-known sauropods, brachiosaurus and sauroposeidon, which have been unearthed in Africa and America.

"The bone contains a wealth of information that allowed us to work out with confidence exactly what sauropod it belonged to. This, coupled with the giant size, was what attracted me to take a further look," Mr Naish said.

One of the neck bones is very well preserved and was found sticking out of a type of sedimentary rock that is known to contain many dinosaur remains - the so-called Wessex Formation. It was well preserved because it was embedded in concrete-like siderite rock - a type of clay impregnated with iron. This protected the fragile bone structure, Mr Naish said.

Sauropods were among the largest land animals to have lived. They were herbivores and probably lived a partly aquatic life. Mr Naish said that until now people did not think that large sauropods lived at this time in Earth's history, a period known as the lower Cretaceous. "The most significant thing about this specimen is that it shows that big sauropods existed in the lower Cretaceous period... I think this is part of a bigger story," he said.

Sauropods were the biggest and heaviest dinosaurs at the time but many experts believed that they had died out by the preceding Jurassic period.

The fossil was found along a stretch of beach between Clinton Chine and Sudmoor Point, and has gone on display in the local Dinosaur Isle museum. Details of the scientific analysis is published in the journal Cretaceous Research.

Mr Naish said he started to study the fossil in 2000. "People knew it was interesting but no one got around to studying it. There are thousands of fossils sitting in collections waiting to be studied but there are not enough experts to do it," he said.

The largest dinosaur in the world is thought to be Argentinasaurus, from South America, a 120ft-long creature weighing up to 100 tons.