Mother’s Day in the UK has been celebrated on the fourth Sunday in Lent since at least the 1500s. For a long time, it had nothing to do with mothers.
Instead, it was the day when people who had moved away from parish churches that they had attended when they were young would return to visit those churches — their “Mother Churches”, if you will. This gave people a chance to reunite with their old friends and their family. They would often bring presents for their mother.
Later the tradition became more associated with actual mothers. People who were servants would even be given the day off to visit their Mums. Church services picked up the theme of giving thanks to and for mothers.
Simnel cake is traditional on this day. It was made by servant girls to give as a present to their mothers when they went home to visit on this day. Simnel cake is also — or rather, mostly — made at Easter now.
In Yorkshire, carlings were made on this day as well, instead of on the following Sunday (the fifth Sunday in Lent) as was the practice elsewhere in England, particularly in the north.
Today is also known as Lætare Sunday in the Church calendar.