The exhibition runs until 11 November.

In those days, there were a handful of people who "occasionally did a tour if somebody asked", he said."You went round with the head guide twice and then you were a guide.

"Today we make [trainee guides] jump through hoops, quite rightly because they're representing the cathedral to large numbers of people."He said that as well as explaining the history of the building, their "core purpose is to talk about the importance of the Christian faith and what that means to people and how it's guided them through the ages".He learned on the job but said even he is "still learning".

"It will usually come about when a member of the public says 'what's that?'," and you go 'Oh what IS that?," he said."It's usually a little detail in a window, or a carving… and, of course, research changes as well."

For example, he explained, 45 years ago the date of the death of Alban was thought to be 209 AD, which was based on a manuscript that had since been proved to be wrong. Now the date is about the year 300 and has been confirmed by archaeology.

"Archaeology is always changing the way we think about things," he said."This support will not only help in preserving the fabric of the cathedral but also invest in the skills and craftsmanship needed to do so," said Dean of Gloucester, the Very Reverend Andrew Zihni.

Part of the work will also include cleaning the masonry and replacing hard cement with traditional lime-based materials more appropriate for the historic fabric of the building."The conservation of Gloucester Cathedral's Cloister is essential in ensuring the cathedral remains safe and beautiful for future generations," said Eilidh McIntosh, head of fabric and property at the cathedral.

"We are fortunate to have a team of highly skilled stonemasons and craftspeople, whose careers have been previously supported by The Headley Trust."They are dedicated to ensuring the work meets the highest standards of craftsmanship."