Why was MI5 created?

Answer 1

The establishment of the Secret Service Bureau

Captain Vernon Kell

In 1909, the Committee of Imperial Defence reviewed Britain's defences against espionage, focusing particularly on the danger to British naval ports from German spies.

At the time, Britain and Germany were engaged in a naval arms race in which the two countries sought to gain technological superiority for their fleets.

The Anglo-German rivalry was reflected in sensational newspaper coverage of German espionage activity, with numerous (and much exaggerated) reports of spies and invasion plots. The Weekly News, for instance, offered £10 to readers to provide information on German agents to its "Spy Editor"; it was quickly inundated with letters reporting supposed German espionage activities.

The War Office and Admiralty agreed to jointly establish a Secret Service Bureau to coordinate intelligence work. Captain Vernon G.W. Kell of the South Staffordshire Regiment and Captain Mansfield Cumming of the Royal Navy were nominated to head the new Bureau, which was established in October 1909.

The Bureau subsequently received an additional requirement from the Admiralty for information about Germany's new navy. Kell and Cumming therefore decided to divide their work. Kell's Home Section took responsibility for countering foreign espionage within the United Kingdom and Cumming's Foreign Section was responsible for gathering intelligence abroad on Britain's potential enemies. These two sections later became the Security Service (MI5) and the Secret Intelligence Service (MI6).

Although Kell had only modest resources at his disposal - by April 1914, he only had fourteen staff - he was able to achieve considerable success against German espionage. Between 1909 and the outbreak of World War I, more than 20 spies were identified by the Secret Service Bureau and arrested.

(Source: https://www.mi5.gov.uk/output/origins.html)