St. Alban's Day

A friend has asked me the following question, which some of your readers may perhaps be able to answer, viz.:— "Till the reign of Ed. VI. St. Alban's Day was kept in England on June 22d (the supposed anniversary of his martyrdom). It was then erased from the kalendar, but restored to it in the reign of Chas. II.; when it was transferred to June 17th. Why was this change made?"