A temporary export ban has been imposed on a 15th Century manuscript because of its "outstanding" importance".
The Wardington Hours manuscript portrays the last hours of Christ
Culture Minister David Lammy placed the bar to give UK buyers the chance to put in offers on the manuscript, called The Wardington Hours after a former owner.
The sum needed is £635,200 excluding VAT, which is the price which the current owner paid at auction.
The 45-page manuscript is decorated in gold leaf and illustrates the story of Christ from betrayal to entombment.
The Wardington Hours comes from the collection of the late Lord Wardington and was created by an anonymous artist known as the Bedford Master.
It was made in the Bedford Workshop in Paris in the early 1400s.
Helen Loughlin of the Museums, Libraries and Archives Council, which advises the government on heritage issues, said: "It has been deemed a national treasure.
"It is of outstanding aesthetic importance. It is very, very beautiful and it is important for the study of manuscripts."
Buyers have been given two months to submit an offer to the private owner of the manuscript, but this deadline may be pushed back if an institution has a "serious intention" of raising the funds.