I could list many quotations from major English writers documenting the various customs of May Day: Malory, Chaucer, Spenser, Pepys, Aubrey, Kilvert, Hazlitt, Dickens - not to mention antiquarians and folklorists for the past 250 years.
The Puritan loathing of maypoles, and their deliberate reintroduction at the Restoration, is well known to historians. There has been singing at dawn on Magdalen Tower, Oxford, on May Day since at least 1674. London sweeps and milkmaids in the 18th century had their Jack-in-the-Greens and their May garlands. It is a date for Morris dancing and for the famous Padstow Hobby Horse.
May queens, May parades and maypole dancing were enthusiastically encouraged by the Victorians, while the more informal gathering of flowers and greenery goes back at least to the 16th century.
All this could be easily multiplied by referring to any standard work on British folklore. The basic context is that of European spring festivals, centuries older than the Labour Day that has hijacked this date.
The Folklore Society
University College London