At DMM the only disaster listed for 1825 in Northern England is 3rd July, Fatfield Juliet Pit.
I’m not advsing you to ignore security warnings, but at a site that you know about from previous visits they usually arise simply because a certificate is out-of-date. I’ve seen quite prestigious sites suffer from this in the past. Judging by the slow speed of loading at DMM, they are operating on a shoestring.
Can you say where they lived so that there is a keyword for newspaper searches?