Unexpected medieval treasures have been discovered in a grave at one of the UK's most beautiful abbeys along with the bones of the abbot they belonged to – probably a well-fed, little exercised man in his 40s who suffered from arthritis and type 2 diabetes.

The discoveries were made at Furness Abbey, on the outskirts of Barrow in Cumbria, a place that in its day was one of the most powerful and richest Cistercian abbeys in the country.

Archaeologists found a silver-gilt crozier (a kind of staff of office) and a jewelled ring in remarkable condition. "This is a very rare find which underlines the abbey's status as one of the great power bases of the middle ages," said Kevin Booth, senior curator at English Heritage.

The discoveries were only made because stabilisation work was needed at the abbey, with wooden foundations giving way and cracks appearing in the walls.

During excavations by Oxford Archeology North to investigate the seriousness of the problem, members of the team came across the undisturbed grave of the abbot together with his personal paraphernalia.

Curator Susan Harrison said it was particularly surprising because the grave had not been disturbed by 16th-century post-dissolution robbers, nor Victorian and Edwardian gentlemen antiquarians. Everyone had missed it until now.

The crozier is unusual and the first to be excavated in this country for 50 years. It has a central gilded silver plaque which shows the archangel Michael slaying a dragon with his sword.

The ring – quite large, probably for a man with big or chubby fingers – is likely to have been given to the abbot on his consecration. "It is an unusual ring," said Harrison. "The bezel is a pyramid shape and is pointed – it would stick in to your finger. You would have felt it when you wore it and it might have been a reminder of the piety of the office."

It is also possible that the ring might have held a relic in place on the abbot's finger.

An examination of the skeleton has shown he was big, overweight, probably aged between 40 and 50, arthritic and "had a decent way of living", said Harrison. There is also evidence that he had later-onset diabetes.

Harrison said the finds were exciting and would help us learn more about Cistercian burial practices in general and Furness Abbey in particular.

The abbey, an inspiration for both Wordsworth and Turner, was founded in the early 12th century by Stephen, later king of England. By the time Henry VIII ordered its dissolution in 1537 it was the second richest in England. The crozier and ring will now go on display at the abbey over the spring bank holiday.