At a treasure trove inquest on Monday he told St Albans Coroner Edward Thomas that he had worked in the field close to Radlett many times but in the past had only turned up coins and small artefacts.

Verulamium museum archaeologist David Thorold told Mr Thomas that the ring dated from the first or second century and probably belonged to a child. It was 90 per cent pure gold and was set with a large garnet. Mr Thorold explained that at the time only Roman citizens were allowed to wear gold. He said "This would be a very expensive article and must have belonged to a person who was in the top five or 10 per cent of the population - the top ruling class." Mr Thorold said that he felt the ring must have been lost by its owner because if it had been deliberately hidden, he would have expected it to have a hoard of other items with it.

Mr Thomas ruled that the find was "treasure" because it was more than 300 years old and contained more than 10 per cent precious metal.

After the inquest, Mr Glenister, who lives in Leverstock Green, said he had been treasure hunting for 15 years and had turned up many coins and other items. He said "I was very excited by this find. It is such a beautiful little thing. I had just changed to a more sensitive metal detector and since I started working with it I have had a lot more success."

Mr Thorold said that the ring would now go to the British Museum and a committee of experts would be set up to determine its value. The British Museum would have first claim on the ring, but he thought it was unlikely they would want it - leaving the way clear for the Verulamium Museum to have it.

Mr Glenister and the farmer on whose land it was found will share the purchase price. The farmer is not being named.