They are shooting scenes for "Jupiter Ascending".
"Staff and volunteers at the cathedral have each received a memo instructing them not to bother the stars, or even make eye contact," femalefirst.co.uk quoted a source as saying.
"It is a real coup for Ely having someone like Kunis filming and they realise how important it is to let her get on with her work without being bothered by overexcited choristers," the source said.
"Kunis and Channing have been squirreled away, and they are being smuggled in so they cause as little bother and distraction as possible," the source added.
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