Witchcraft Trial

When Lumsden tells Hannay that his wife had been sent to prison for 4 years for practising witchcraft it is a reference to the real case in 1944 of Helen Duncan, the last person to be convicted of witchcraft in the UK, although she only received a sentence of 9 months and the offence was in effect of being a fraudulent medium, which Hannay is quick to spot in the "seance" Mrs Lumsden conducts in the film:

https://en.wikipedia.org/wiki/Helen_Duncan