The recent incident on board an American jet when the crew mistook a passenger laying tefillin for a suicide bomber is not the first time the little black boxes have caused suspicion.

The Jewish Military Museum in Hendon has a letter written from the trenches of First World War by Lt Marcus Segal of the King’s Liverpool Regiment.

He recalls being asked to investigate two German prisoners who were believed to be carrying secret signalling equipment — only to find the mystery items to be two pairs of tefillin carried into battle by their Jewish owners.

Sadly, Lt Segal was killed in action in 1917.