Arthur Owens (SNOW) Sir John Masterman Twenty Committe XX

120 German agent in Britain were located, 17 were executed and one commited suicide.
The agent’s communication with the Abwehr was completely vetted by MI5’s Twenty Committee.
John Masterman was at the helm of the Twenty Committee (Later became Sir John Masterman).
They would allow some truth's to be told but nothing vital, and plausible false information carefully selected.

Occasionaly when falsified information was sent to Kuehlanthal, events would make them realise that the information was completely fabricated. On these occasions he would let Kuehlanthal know that one of his agents was responsible and would be dealt with. He would let Kuehlanthal know his name and tell him that he would have him killed off.
Garbo would simply get a news article put into the newspapers about the assassination, knowing that Berlin would get a copy.
This gave Garbo even more credibilty, the fact he could have people in England killed for the German cause.

One of Garbo's agents (William Gerbers) was supposedly in Liverpool at the time when a fleet of ships were leaving Liverpool on a secret mission to North Africa..
The problem being that there was no way that the agent would not report something as significant as this, but this information could not be passed on to Berlin.
Garbo came up the an idea to kill off the agent and even put a death notice in the newspapers.
He informed the Abwehr about his agents death and told them he would try and get another agent for the North West as soon as possible.
The Germans were so sympathetic that they sent him more money to fund the search, and also sent money for the dead agents family.
By this time Hitler was aware of Garbo's exploits and was delighted to have his communiqué.
Berlin even stopped sending spies into Britain because of the amazing network that Garbo set up.

In 1938 Arthur Owens while travelling in Germany was contacted by the Abwehr regarding feeding them information, Owens a Welsh electrical engineer and civilian employee of the navy.
Owens went along with the Abwehr to be a German spy in Britain. When he returned to England he reported the meeting with the Abwehr to MI5.
MI5 confiscated his radio transmitter and put his name in a list of suspected people to be detained in the event of war.
At the outbreak of war Arthur Owens was indeed detained but also established contact with the Abwehr in Hamburg with a prison warden as his supervisor.
MI5 had it’s first Double Agent (Codename SNOW).

Whenever Berlin sent one of it's agents to Britain they would tell them to contact SNOW, and likewise would let SNOW know that he was coming.

All German agents were intercepted as they arrived in the country and used as double agents and were given names like Balloon, Bronx, Brutus, Careless, Carrot, Dragonfly, Lipstick, Mullet, Mountain, Mutt and Jeff, The Snark, Sniper, Steeple, Teapot, Tricycle, and Zigzag.