Thomas Tallis (1505 – 1585 by the Julian calendar still then in use in England) was an English composer who occupies a primary place in anthologies of English choral music, and is considered one of England's greatest composers. He is honoured for his original voice in English musicianship
This lovely melody by Tallis comes from the Mulliner Book, a collection of British renaissance keyboard music.
It is almost certainly an arrangement of an unaccompanied vocal original.
The nature of the piece presents the opportunity to make the harpsichord really sing in long, lingering, broken chord sequences.