The team, backed by volunteers from Renfrewshire Local History Forum, is carrying out a 12-day excavation of an ancient drain that lay undisturbed until its discovery in 1990. An initial excavation revealed an arched corridor almost 6ft high, and uncovered pottery fragments and gaming pieces, a complete chamber pot, and other artefacts.

This month’s dig is the first subsequent excavation of the drain, which dates to at least the fifteenth century.

Archaeology professor Steven Driscoll, part of the Glasgow team, said the site was uniquely well preserved. “What’s unusual is that it hasn’t been messed with. This is a loo that hasn’t been flushed for 500 years. We have a kind of sealed environment, containing artefacts like the earliest known piece of Scottish music, which we found scratched into pieces of slate.

“The monks here were part of an internationally connected order. They were using Paisley as a kind of communications centre – as we can see from these tags we’ve found, which were the binding of boxes being shipped to the continent.

“We’ll be finding out about the sorts of things that were growing in the gardens, and the things they were eating. So it’s possible to reconstruct the lifesyle of the monks.” Paisley Abbey was founded as a Cluniac priory in 1163, and became an abbey in 1245. The monastery was disbanded at the Scottish Reformation, in 1560, when the monastic buildings were handed over to the Hamilton family.

Andrew Eadie, of the Renfrewshire Local History Forum, said the excavation had been timed to link with next year’s Europe-wide celebration of the Cluniac monastic order’s 1100th anniversary.

“One of our aims is to make people in Paisley, and elsewhere in Scotland, realise that Paisley’s heritage goes back far longer than most people realise. Everyone thinks of Paisley as a mill town, but few know about the Paisley drain,” he said.