From The Public Records Office Security Service Releases 1941-45.
George William Armstrong (George Hope) (KV 2/28, KV 2/29, 2 files)
A British subject, resident in the US, who offered to help the Germans as expressed through a letter sent to the German Consul in Boston, Dr Herbert Scholz in the autumn of 1940. In it he offered to return to England and obtain information in the German cause. The attempt was discovered and Armstrong was arrested and later returned to England for trial. The trial case papers include statements on the case, transcripts of proceedings during the trial at the Old Bailey on 6-7th May 1941 and the judgement of the court of appeal which considered the appeal against the death sentence imposed. This file also includes copies of the letters and exhibits (including a steel sample obtained for industrial intelligence (KV 2/28).
The second file (KV 2/29) includes accounts of his arrest in February 1941 when he was deported to Britain and numerous background reports. He was executed in July 1941, the first German spy of the war of British nationality
Stephen Stratford includes a more detailed account here.
The text of his statement to the police is here.