An AVRO manufacturers plate is riveted to the cover and inside are many pictures of an all (predominently) femail workforce.
I am in the initial stages of research but will post what I know in the hope of further information.
The factory was in Leagrave, just outside Luton in Bedfordshire and was called the Omnia Works. They are listed as Aeroplane Manufacturers and Aeronautical Engineers, Contractors to HM War Office and Admiralty.
All aircraft appear to be Avro 504's and numbers visible are as follows.
F9773, F9772 F9767.
The Hewlett family appear to have been early aviation pioneers, both Mr and Mrs Hewlett worked at the factory and a son is listed as a "famous airman"
I will post all the pictures as soon as time allows. Any help greatly appreciated