The regimental War Diaries are held at The UK National Archives and as of April 2020 have been made available for free download*. They are the official unit war diaries for the British Army that contain records of daily activities, including casualties. They are not personal diaries.
* you will need to register for an account and login to get access to the downloads. When following the link from any record be sure to make a note of the page number. You will then have to download the full diary in pdf format and search for the respective page and hence entry.