A letter written by Albert Einstein, in which the renowned physicist described religious beliefs as "childish superstitions", has been sold at auction to a private collector for a record breaking £170,000.

Hopeful bidders packed the room at Bloomsbury Auctions in Mayfair, which installed an additional 11 phone lines to cater for demand from international buyers.

Bids rapidly soared beyond the guide price of £6,000 to £8,000.

The letter was written to philosopher Eric Gutkind in January 1954 a year before Einstein's death. The Nobel physicist described God as the "product of human weakness" and the Bible as "childish".

"The word 'God' is for me nothing more than the expression and product of human weaknesses, [and] the Bible a collection of honourable but still primitive legends which are nevertheless pretty childish," said Einstein in the letter.

Einstein also dismissed the notion that the Jews are God's chosen people. " As far as my experience goes, they are no better than other human groups, although they are protected from the worst cancers by a lack of power. Otherwise I cannot see anything 'chosen' about them."

Bloomsbury Auctions spokesman Richard Caton said that the auction house was "100 per cent certain" of the letter's authenticity.

Einstein was born into a Jewish family in Germany in 1879 and started questioning conventional religion at the age of 12 after going through a devout phase in his early years.