The relic, a fragment of bone thought to come from Becket's arm, is coming all the way from Hungary's Esztergom Basilica, where it has been venerated for almost 800 years.
Hungary's President Janos Ader and Cardinal Erdo, Archbishop of Esztergom-Budapest, Primate of Hungary will attend a celebratory mass in London's Westminster Cathedral
The bone fragment will then be put on display at Westminster Abbey
and St Magnus the Martyr Church
in London, Rochester Cathedral
-- site of Becket's murder -- before being returned to Hungary.
"Who will rid me of this troublesome priest?"
Thomas Becket was a priest, who became Archbishop of Canterbury in 1161, during the reign of his friend, Henry II.
In 1170, when their friendship soured over dissensions between the Church and the monarchy, the king is reputed to have asked: "Who will rid me of this troublesome priest?"
A short time later, Becket was murdered by four knights inside Canterbury Cathedral
Becket was canonized in 1173 and the first shrine dedicated to him, in the cathedral where he was killed, attracted pilgrims from around Europe, including Hungary.
In 1220, when his tomb was opened and moved to a different burial place inside the cathedral's Trinity Chapel, it is rumored that two Hungarian priests were present.
It is thought they may have taken the hand fragment back to Hungary, but exactly how it got to its present home remains a mystery.
Becket became particularly important to Hungary in the 20th century, during the country's communist regime, when he was seen as a symbol of resistance against the State's interference in the Church.
The pilgrimage to Thomas Becket's tomb became so well known that Geoffrey Chaucer used it as the background to "The Canterbury Tales
Becket's shrine was destroyed in 1538, on the orders of Henry VIII.