May Day was one of the most important days of the year, as it celebrated the end of what were then very long, cold winters. Here’s some accounts from The Streets of London by Thomas Burke:

Of the annual feasts those of May, Midsummer and Christmas were the most marked by pageant and ceremony. On May Day all citizens, young and old, went into the fields to pluck flowering May and green branches, with which they decked the streets and their homes, following the pagan ritual of bringing Flora to the hearth. May-poles were set up in each parish, often of immense height – the church of St Andrew Undershaft got its name from the fact that the may-pole of Leadenhall Street over-topped its tower – and the girls and the morris dancers, garlanded with flowers, danced round them and their Queen. In the evening, bonfires were lit and masques were performed. May Day meant much more to them than it did to those of later centuries, since their winter was indeed a winter. For the poorer people , with little money fo fuel and light, winter was a season of some months of confinement in their homes after sunset, of going to bed early and getting up in darkness, and of shivering though the day, and living on salted foods. May Day meant release from that confinement; it meant light and air and warmth and easy living; so that when it came it was not taken for granted: It was met with due salute and thanksgiving.

The above Maypole was set up by the masters and governors of the city, erected on Cornhill. But on May Day 1517 a dangerous riot took place, resulting in the murder of several foreigners; two ringleaders were  hanged for this.

By the 18th century, it had become akin to Boxing Day, when tradespeople dressed up in to visit customers.

The ruddy milk-maid exerting herself in a most sprightly manner under a pyramid of silver tankards, and like the virgin Tarpeia, oppressed by the costly ornaments which her benefactors lay upon her. these decorations of silver cups, tankards, and salvers, with the addition of flowers and ribbands, which the maidens carried upon their heads when they went to the houses of their customers, and danced in order to obtain a small gratuity from each of them.

But there were always those who objected to ordinary people enjoying themselves. It is hard to separate the truth from this condemnatory account:

Against Maie, Whitsondaie, or some other time of the year, every parish, town, and village, assemble themselves together, both men, women and children, old and young, even all indifferently; and either going all together, or dividing themselves into companies, they go some to the woods and groves, some to the hills and mountains, some to one place, some to another, where they spend all the night in pleasant pastimes, and in the morning they return, bringing with them birch boughs and branches of tees, to deck their assemblies withal. And no marvel, for there is a great lord present among them, as superintendent and lord over their pastimes and sports, namely, Satan, prince of hell. Bt their chiefest jewel they bring from thence is their Maie pole, which they bring home with great veneration, as thus: They have twenty or forty yoke of oxen, every ox having a sweet nosegay of flowers tied on the tip of his horns, and these oxen draw home this Maie pole (this stinking idol rather) which is covered all over with flowers and herbes, bound round about with strings, from the top to the bottom, and sometime painted with variable colours, with two or three hundred men, women and children following it with great devotion. and thus being reared up, with handkerchiefs and flags streaming on the top, they strewe the ground about, bind green boughs about it, set up summer halls, bowers, and arbours hard by it; and then fall they to banquet and feast, to leap and dance about it, as the heathen people did at the dedication of their idols, whereof this is a perfect pattern, or rather the thing itself. I have heard it credibly reported by men of great gravity, credit, and reputation, that of forty, three-score, or a hundred maids going into the wood over-night, there have scarcely the third part of them returned home again undefiled.

Claims were often made that young women became pregnant at fairs and other celebrations, but the parish registers do not support this.