The code-breaking challenge is the fifth by the Cheltenham-based operation to test the mental skills of would-be operatives.

A spokesman told the BBC that GCHQ was expecting a good response after the success of the last challenge set.

Full details of the challenge - which is in three parts - can be found on GCHQ's website.

Big Bang

The spokesman added: "We are expecting a lot of replies during the holidays when people are off work."

Visitors to the site are presented with a two columns of codes, one a list of men and the other a list of women.

They must decipher the names, connect the two columns in two ways and find the hidden quotation.

Six winners, picked at random, will be presented with a copy of Big Bang by Simon Singh.

A hint to the challenge will be published in the New Year, with answers on the website on 7 February.