Hello Doug377train and welcome to forum. You must live quite close to me as I live in St Leonards!
Have you heard about South East Rail Gen? It's a Yahoo based railway information site for the London and South East area. Times for test trains around the LSE area are regulary posted on SE Gen as well as railtour times, freight/engineers trains and other unusual, one off and rare moves.
http://finance.groups.yahoo.com/group/se-gen/
Hope this helps.