http://www.uktrainsim.com/
Mainly steam locomotives admittedly, though there are a couple of diesels for RS, not least a Hymek.
Duff cab and sounds though if im not mistaken
http://www.digitaltraction.net/mainsite/index.php?option=com_docman&task=cat_view&gid=42&Itemid=58
Class 25 sounds recomended, its miles better with them