Gandalf actor's warning to schoolchildren if they don't revise: You Shall Not Pass

Lord of the Rings actor Sir Ian McKellen has delivered a stirring motivational message to students, warning them: "If you don't do your revision properly, do you know what will happen? YOU SHALL NOT PASS!"

The line is famously boomed out by the wizard Gandalf in The Fellowship of the Ring, although J.R.R Tolkein had not written it in the original book.

The veteran of stage and screen was at a specialist performing arts college in Somerset when the clip was recorded.

The students at Chew Valley School gave McKellen a rapturous reception - although whether his message spurs them to exam success remains to be seen.

Watch the clip from the Lord of the Rings film here: