Pedant alert:~ It should be the 29th of May, the day otherwise known as 'Oakapple Day' and the tune is often called 'Royal Oak' as it was the anniversary of the restoration of the Monarchy, Charles II hiding in the oak tree and all that. it's also available as a morris dance.

The Hayley Westernra is indeed the John Rutter arrangement. Harry Secombe (or Sir Cumference as he referred to himself) is singing 'Royal Oak'. It's available in many hymn books: Songs of Praise, Hymns Ancient and Modern Revised, Celebration Hymnal and Songs and Hymns of Fellowship should all have it.

LTS