On December 16 1910 a gang of robbers attempted to dig their way into the premises of a jewellers' shop at Houndsditch, in the City of London. Armed, it turned out, with an assortment of pistols and large quantities of ammunition, the gang was disturbed, the police (who were unarmed, of course) were called, and in the ensuing confrontation three officers were killed and a further two severely disabled.

Two weeks later, following a tip-off, the Metropolitan Police surrounded a house in Sidney Street, Stepney, where two of the gang were believed to be hiding. Winston Churchill, then Home Secretary, took personal charge and called in a detachment of the Scots Guards.

There was a sensational gun battle. A bullet went straight through Churchill's top hat. Somehow the house caught fire, but on Churchill's orders the fire brigade stayed away. When the fire eventually burnt itself out, the charred remains of two of the robbers were found inside.

In due course seven other of the supposed robbers and their alleged accomplices were brought to trial, but all were acquitted or had the charges against them dropped. Churchill himself was heavily criticised for his intervention. But he seems to have revelled in the publicity, which strengthened his image as a tough devotee of "law and order".

So much for the basic facts of the Houndsditch murders and the so-called Siege of Sidney Street. These dramatic events at once entered the public imagination. But who were these robbers? Were they just common jewel thieves? Or did they have a more sinister agenda? Speculation was rife at the time, and has continued ever since.

The core members of the gang were identified as Latvian (that is, Russian) refugees. How many of them were ethnically Jewish we do not know, but it is a safe bet that some were. At the time, in the popular imagination, they were identified as Russian anarchists. That they were anarchists, in the true sense of the word, is highly doubtful, but credence appeared to have been lent to this conjecture by the fact that some gang members were known to have frequented the Workers' Friend Club established in 1906 in Jubilee Street, Whitechapel, by the German gentile anarchist, freethinker and philosemite, Rudolf Rocker.

The truth was that many Russian refugees, Jewish and non-Jewish, drifted through the Jubilee Street club. Few embraced anarchism as a cause. However, the bomb-making activities of European anarchists had already become the stuff of legend, fictionalised in Joseph Conrad's 1907 novel, The Secret Agent.

The supposed leader of the Houndsditch gang was identified by the press as "Peter the Painter" - said to be the alias of one Peter Piaktov, a Latvian-born Bolshevik. Did "Peter the Painter" really exist? No one knows. One of those put on trial and acquitted was Ya'akov Peters, whose flat may have been used by gang members. Peters subsequently returned to Russia and, after the Bolshevik Revolution, became a founder of Cheka, the forerunner of the KGB. But whether Peters and "Peter the Painter" were the same man is doubtful; there is no hard evidence to link the two.

What is certain, however, is that the Houndsditch murders and the Sidney Street siege rekindled a public debate that had been simmering for the past quarter-century. Free trade - the freedom to import and export at will, and the freedom of persons to move in and out of the United Kingdom at will - had been cornerstones of British economic and social policy since the mid-19th century. Popular wisdom held them to be the foundations of Britain's phenomenal commercial expansion.

But as other nations underwent their own industrial revolutions, and imposed duties on British goods, and as unemployment grew in Britain as a result, free trade came under scrutiny.

In London's East End, and in the Jewish quarters of other cities, such as Manchester and Leeds, this scrutiny dovetailed with crude, politically-motivated anti-Jewish agitations. In 1901 the British Brothers' League was formed to demand a restriction on the immigration of "aliens" (ie Jews) into the UK, and in 1905 the Conservative government passed the Aliens Act - the foundation of modern immigration legislation. This measure sought to curb the right of "pauper aliens" to settle in the UK, and of "persons of notoriously bad character."

There was a surprising amount of Anglo-Jewish support for this measure. Chief Rabbi Hermann Adler was especially reluctant to condemn it. "We must frankly agree (he later wrote) that we do not desire to admit criminals and that there is force in the argument against the admission of those [Jews] mentally or physically afflicted."

Opposition to the Tory proposals was left to a handful of Liberals, in particular Winston Churchill, who was busily wooing the Jewish electors of north-west Manchester, for which he became Liberal MP in 1906, the year in which the Liberal party won a spectacular General Election victory. Happy to oppose anti-aliens laws when out of office, the Liberals now made it clear that they had no intention of repealing what they admitted had been a very popular piece of legislation.

Churchill himself had a political career to think about. In 1908 he was promoted to the Cabinet as president of the Board of Trade, and in February 1910 he became Home Secretary. His extraordinary intervention at Sidney Street seems to have been calculated to project a particular media image. Subsequently he let it be known that further anti-immigrant legislation might be necessary, and in April 1911, four months after his appearance at Sidney Street, and enjoying the publicity it had brought him, he brought in a bill designed to redeem this pledge. Thankfully for Jewish refugees yet to arrive in Britain, it was never passed.