A fascinating letter by Albert Einstein revealing how he was enjoying the 'enviable solitude' of Norfolk while in hiding from the Nazis has emerged 92 years on.

The genius mathematician first fled to Belgium after Adolf Hitler came to power and Jewish people began to be targeted.

Although he had police protection, Einstein was still deemed under threat there, so he travelled by boat to Dover and was then driven to the Norfolk coast.

His alien new surroundings as a guest of Conservative MP Oliver Locker-Lampson consisted of a tiny 9m sq hut consisting of a single room.

But despite the lack of luxury in the cabin on Roughton Heath, near Cromer, Einstein informed son Eduard that he was enjoying his new surroundings and was spending most of the time doing maths.

He added that, whenever he was cold, he would run around outside to warm up.

Einstein started his letter to his son by confiding in him that he was aware of 'plans for my assassination'.

He then cuttingly described the Nazi takeover of Germany as 'a revolution of the stupid against the rational'.

Einstein added with gallows humour: 'It's a shame that an old fellow like me cannot have his peace and quiet.

'When you're dead, you don't get to enjoy it, unfortunately.'

Einstein was on a visiting professorship at the California Institute of Technology CalTech the Nazis assumed power in Germany early in 1933.

He was immediately personally targeted, with several raids on his flat and country house.

When he landed in Antwerp on his return to Europe on March 28 he formally renounced his German citizenship.

He remained in Belgium over the summer, but the threat of violence from the Nazis increased, particularly after the assassination of the philosopher and anti-Nazi figurehead Theodor Lessing in Czechoslovakia in August 1933.

In early September, Einstein secretly escaped to England, where he was given shelter by Locker-Lampson.

Although his whereabouts were intended to be secret, photographs of Einstein, guarded by locals with shotguns, were published in the newspapers.

He received a small number of visitors at Roughton, including the sculptor Jacob Epstein who he sat for for a bust.

On October 7, Einstein boarded a ship for the US, where he had been offered a position at the Institute for Advanced Study in Princeton, New Jersey.

He never returned to Europe before his death in 1955.

The two-page letter in German, signed 'Papa' and sent from Cromer on September 23, 1933, reads: 'Times have been rather turbulent since my last letter.

'It was actually reported in the newspapers that there were plans for my assassination.

'As a result my police protection in Belgium was increased so much that I did not want to bother any more.

'So for more than three weeks now I have been near the English coast in enviable solitude.

'My little house, in which I live alone, has an area of roughly 9 m2 and consists of a single room.

'Outside the door you have immediate access to Mother Nature. I spend most of the time doing mathematics and run around outside when I get cold.'

The letter, which remained in the Einstein family until 2001, is now being sold by a private collector at London-based auctioneers Christie's with a £18,000-£25,000 estimate.

The auctioneers say this is one of a very small number of letters Einstein wrote while temporarily resident in England.

Thomas Venning, books and manuscripts specialist at Christie's, said: 'It's a lovely example of Einstein's sense of humour, even in the most stressful possible circumstances.

'He is at serious risk of being assassinated by the Nazis, but still gets in a joke about how you get plenty of peace and quiet when you're dead, but sadly don't get to enjoy it.

'His opposition to the Nazis was significant: the line in the letter about the victory of Nazism being the 'revolution of the stupid against the rational' was one that he reused in later years, and the Nazis knew that his international prominence and unstinting criticism of them was a threat.

'The other theme in the letter is his love of peace and quiet and his love of nature: in some ways being stuck in the middle of nowhere in a one-room that is quite a dream scenario for Einstein.

'He really asked nothing better than being left alone to think about science, with the minimum of creature comforts.

'Of course, there is something slightly incongruous about a world-famous figure like Einstein hiding out in a hut in the Norfolk countryside, and there is something slightly Dad's Army-like about the photographs of him sitting outside his hut, guarded by locals with shotguns.

'The fact that these were published in the British press at the time somewhat reduced the effectiveness of his 'top secret' hideaway.'

The sale takes place on July 9.