It was a particularly difficult moment for Major James Robertson, head of MI5's Middle East section, when Ernest Bevin decided, in 1946, to pay a visit to Egypt.

As if that year's blowing up of the King David Hotel in Jerusalem by Jewish insurgents had not been enough, his desk was littered with agents' reports, all carrying the same deadly message.

Jewish militants, they said, some believed to be already in Britain, were planning to assassinate leading British politicians - and top of their list was the fiercely anti-Zionist Foreign Secretary,

The warnings, among MI5 documents released this week, did not go unheeded. An attempt on Bevin's life was "almost a topic of household conversation in the Middle East," said one top secret cable.

Elaborate security measures were suggested. It was recommended that Bevin should spend most of his time in Egypt aboard a Royal Navy vessel, in Alexandria harbour.

His few public appearances would be protected by Egyptian troops, together with a British escort company comprising jeep-borne soldiers, armed with automatic weapons.

MI6 agents would watch out for signs that what officials described as "Eastern Jews," had infiltrated Egypt. In addition, to mislead would-be assassins, armed guards were placed at buildings and airstrips not being used during the visit.

However, it was a number of intelligence reports from Palestine that were of greatest concern to Whitehall. They warned that the militant Stern Group and Menachem Begin's Irgun were preparing for action in the UK.

A report, marked top secret, recorded a big rise in membership of the Stern group and said it was "planning to carry out the assassination of important persons in England."

The targets, said the agent, would be prominent British supporters of the Arab cause rather than cabinet ministers. But then came a second report, warning that ministers, including Winston Churchill and Bevin, "were possible objects of Stern Group attention."

An MI5 cable said an informant, formerly attached to the right-wing Zionist Betar movement, had told them that Stern agents could already be in Britain.

A plot to kill Bevin was being "hatched by representatives of Irgun and the Stern Group which would be carried out by sympathisers," he had told MI5.

In an effort to identify the "sympathisers," agents pored over the pages of a revisionist newspaper printed in Manchester. But this proved fruitless.

As MI5 attempted to track down reported infiltration by terrorist groups and monitored the actions of British Jews thought to be supporters of the militants, there was criticism in diplomatic and intelligence circles about Bevin's fervent opposition to Jewish aspirations for a homeland.

In a secret cable from Jerusalem to Special Branch officers in London, an official suggested that the "intensification of terrorism may in part be due …to a speech (at the 1946 Labour Party conference) by Mr Bevin. His harsh remarks … have caused considerable bitterness among the Jews.

"The average Jewish man in the street in Palestine would describe it as the most antisemitic speech to be delivered by a British minister."