The ancient druids of Britain celebrated Beltane around May first. It was actually celebrated on the cross-quarter day, which is the day exactly between Spring Equinox, the day when day and night are exactly equal, and Summer Soltice, the longest day and shortest night of the year. When the Romans occupied the British Isles, they celebrated the five-day feast of Floralia, from April twenty-eighth to May second, in honor of Flora, the Roman goddess of flowers.
By the fourteenth century, various aspects of the two celebrations have combined and villages in Southern England are celebrating a spring festival on May first and dancing around the tallest tree in the village or a pole festooned with flowers and ribbons in the village square. Chaucer makes mention of a maypole in his writings. Scotland and Ireland also celebrated May festivals but had village bonfires rather than maypoles.
Maypole dancing was outlawed during the Reformation. The festivals were un-Godly with mixed gender dancing, flirting, drinking of alcohol and general merry-making. They were re-instated during the Restoration by Queen Mary and Queen Elizabeth, who both liked them.
While the dancing around the May pole was usually a country-style dance with men and women weaving in and out among each other, the concept of holding ribbons and winding them around the pole while dancing is actually post-period. A playwright named J.T.Harris wrote "Richard Plantagenet" in 1836. One of the scenes had a maypole with long ribbons on stage and the dancers wove the ribbons as they danced. The fad caught on and soon every village was dancing with ribbons around the maypole.. The maypole dance was usually done by adults. It isn't until the 1930's that it becomes known as a children's activity.
Morris dancing was often done on May Day celebrations. The actual origins of the dance are lost in antiquity, however the most common theory is that it was based on the Morisco dance of the Spanish Moors and brought to England around 1360 A.D by John of Gaunt, the brother of Edward the Black Prince. Another theory is that it's from the 12th century Italian Moresca dance. The earliest known reference is a 1458 will which bequeaths 'a silver cup sculpted with morris dance'. This is not the only such cup known to be in existence. William Shakespeare had a morris dance in "Henry V". The dance was performed before Henry VIII and Elizabeth I and was referred to as an "ancient country dance" then.
The dance varies from village to village, each town doing their own unique rendition of the dance with little in common between them save for a similarity in costumes and props. In some villages, it's an exhibition only with only a handful of dancers. In other villages, it's participatory with literally hundreds of dancers joining in.
Traditional costumes include men dressed in white with colorful ribbons on their shoulders and bells on their legs and arms to emphasize the movement of their limbs with the ringing. They would dance with swords and pantomine a battle against men whose faces were blackened with burnt cork, lending some credence to the theory that the dance originally commemorated Charlemagne's battles against the Spanish Moors. Some dancers wore wire frameworks around their waist, decorated to suggest horses. The children's toy hobby-horse of a wooden horse head on the end of stick were patterned after this traditional morris costume.
In Elizabethan times, Robin Hood tales were popular and the characters of Robin Hood, Maid Marian, Little John, Friar Tuck, Tom the Piper, (a musician with pipe and tabor) would be participants of the dance. The traditional fool's costume was often seen as well as multiple dancers protraying a dragon which would often be ritually slaughtered by the dancers.
Traditional music for morris dancing was pipe and tabor (a small drum), fiddle, squeezebox, tambourine and rhythm sticks with bells. Modern performances have been known to have virtually any instrument including saxophones and guitars.
Morris dancing started dying out during the Industrial Revolution. Rural traditions were abandoned as people started moving to larger cities for economic opportunity. Today the participatory versions of morris dancing are all but extinct and the dance survives today only as an exhibition dance.