Previously restricted reports from MI5's first ten years throw light on the shadowy characters suspected of spying during the first world war. John Davies reports

On 11 April 1915 Ludovic Hurwitz y Zender, a Peruvian businessman, arrived in Newcastle upon Tyne by boat from Christiania (now Oslo). Apparently intent on buying tinned fish on behalf of a firm of importers in Lima, he then headed northwest into Scotland. In Glasgow he "led a very quiet life, walking the golf links with the manager of the hotel, going twice down to the Clyde on a Sunday but not appearing to have any business friends".

We know this because he was watched by agents of the newly formed Secret Service Bureau (later MI5), a summary of whose reports on Hurwitz and other suspicious characters is now available for the first time. For the price of a CD-Rom (Pounds 99) or the cost of a trip to the Public Record Office in Kew, you can look at previously restricted material from MI5's first ten years to 1919 and get a flavour of the British counter-espionage and counter-subversion effort of the first world war.

Using some of this material, last week's Timewatch (BBC2) surveyed the early days of MI5 and its forceful but secretive first head, Vernon Kell. Transmitted the day after the files were "released", the programme recounted some of Kell's triumphs over the German spymaster Gustav Steinhauer, particularly in the years immediately after the passing of the 1911 Official Secrets Act.

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Under headlines such as "Farcical secrets of the early James Bonds" and "How Major K unmasked German 'birdwatchers'", last week's newspapers also made the most of the titbits a day's reading of the files could offer - though they seemed to doubt whether the British back then really needed to worry about German spies. Did memos warning that "espionage is carried out wholesale in East Anglia, as is well known by everyone who rides a bicycle about those counties in the summer" really get taken seriously? Were files instructing agents on how to make "invisible ink" with such homely ingredients as lemon juice more than a joke? Only the material on Ireland and Germany's suspected contacts with Sinn Fein was taken seriously by the newspapers - no doubt reflecting current British concerns.

For much of the information in these files is already in the history books. Perhaps, then, the value of the files is in the detail; the glimpses of individuals trying to make sense of their lives in the chaos of war. They emerge briefly and then disappear, as if in a fog.

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Certainly one learns more about Hurwitz - for instance, how he sent five telegrams to Oslo from Glasgow. "Ostensibly they were orders for different classes of tinned fish goods, but the wording of the messages varied suspiciously," reads the report of the Secret Service's G Branch. One learns, too, that in Norway the telegrams' recipient, August Brockner, was shadowed by an agent "who saw him deliver a large envelope at the private house of the German ambassador"; while back in Peru it was established that the firm for which Hurwitz was travelling "had no standing or credit and was connected with the Germans". Eventually thanks to "the destructive criticism of an expert in the fish-trade" Hurwitz was revealed to be an impostor; his orders for fish "out of season, in wrong quantities and packings" must have been coded messages. So the surveillance was worth it.

But one is less sure about other names in the files. Take the Black List developed by MI5 from its earlier register of aliens - an example that survives is Volume 14, from 1918, a sort of Who's Who of agitators, chancers and the demi-monde in the second decade of the century. One almost feels sorry for people such as "Olympe Lambert nee Guillot or Guillot or Nuillet", domiciled in Lausanne but apparently at large in France in 1918. After identifying two of her lovers, the Black List notes she was "expelled from Lyons where she made constant efforts to get into relations with French and British officers" and "is considered dangerous".

Or there is William Rosenblatt, an "American Jew, went (to) Russia early in 1917 via Japan, ostensibly as representative of United Exchange Corporation and New York Tribune". Classed as an "instigator of hostile or pacifist propaganda" and therefore forbidden to enter Allied territory, he was "believed by police to have stolen jewels and objects of value from museums and royal palaces in Russia". The worst that could be said about him, however, appears to be a June 1918 report that he was "most unprincipled, is believed to be carrying on intrigue with enemy".

We also find out what happened to Ludovic Hurwitz y Zender. Arrested later in 1915 after returning to Newcastle from Norway, he was tried by court martial "on four charges under DRR (Defence of the Realm Regulations) section 48, eg of having twice committed a preparatory act in coming to England - and of having twice attempted to communicate information by sending a telegram". The Peruvian's telegrams, in the G Branch report's words, "having been satisfactorily deciphered contained true information with regard to ships in the Firth of Forth". And as further proof of his guilt, he was carrying "a bottle of medicine which was afterwards found to be Protargol - a medium for secret writing".

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Having been found guilty, he was shot on April 11 1916, one year after first setting foot on British soil. That's what happens to spies.

MI5: The First Ten Years, 1909-1919, Public Record Office Publications, price Pounds 3.99.