The source is The Army Roll of Honour 1939-1945, an original document held under shelf reference WO304 at The National Archives, now decoded and put into a searchable database. It contains the details of British Army casualties during World War 2.
The original 41-part document is in two main sections, firstly by regiment and secondly by surname.
The document also includes a key to the codes used in the main sections. The key is necessary as much of the information in the original text is coded. The coded text includes the army rank, the corps in which the serviceman or woman served, and their places of birth, residence and death.
All credits: infantry, the artillery and all supporting corps.
All ranks: officers, non-commissioned officers (NCOs) and other ranks are all included. You do not need to know the rank of the soldier you are looking for. The rank shown is that held at death.
All areas: soldiers from all parts of the UK are included.
Only serving soldiers are included. If a soldier died after having been discharged from the army, even if their death occurred due to wounds incurred during their army service, they will not be included here. Usually their death will be included in the relevant civil death registers for England and Wales, Scotland or other jurisdiction of death.
The records include those who were killed in action, died of wounds, and died of disease or other (including natural or accidental) causes. Soldiers who were recorded as missing presumed dead are also included.
Please note that the records exclude most of the soldiers who were court-martialled and upon whom death sentences were executed. This is because such personnel were regarded as having died dishonourable deaths and therefore it was not thought appropriate to include them in a roll of honour alongside personnel who had died honourably for their country.