The oldest surviving copy of the Bible will leave the British Library for only the second time since 1933 when it is lent to the British Museum in October.

The Bible, known as Codex Sinaiticus, dates back to the fourth century AD and will be part of a display in the British Museum exploring 1,200 years of Christian, Jewish and Islamic faith in Egypt after the pharaohs.

The codex contains the first complete copy of the New Testament and is considered one of the world's most valuable artefacts.

"Since it arrived in the 1930s it has always been one of the greatest treasures in the collection," said Scot McKendrick, head of western manuscripts at the British Library.

"It is quite phenomenal they they are able to lend it to us," said Elisabeth O'Connell, assistant keeper in the British Museum's department of ancient Egypt and Sudan. "We are absolutely thrilled."

The codex was bought by Britain in 1933 from the Josef Stalin's Soviet government who were desperate to raise cash for the second five-year plan.

The only other time the codex has left the British Library's building when it was moved to a specially built cave in Aberystwyth for safekeeping during the second world war.

The major exhibition will explore Egypt's progression from being a pharoah-worshipping society, to becoming majority Christian and then majority Muslim. It will argue that the transition from worshipping many gods to one God shaped the modern world as we know it.

The ancient manuscript will be displayed alongside two founding texts of the Hebrew and Muslim faiths.