Sorry to butt in, but I am looking for you too, on Ancestry. I can see the marriage and death dates you mention in the indexes.
I won't be able to get you an exact date (maybe LeChatROuge will), but while I'm here ... I can see him in the birth indexes for the first quarter of 1860 (which could also mean a birth very late in 1859, registered in Jan, I beleve). District of birth is Horsham, Sussex. In order to get the exact date, I think you might need to order the certificate - unless Free BMD has more info available than I am aware of (I don't use it much as most of my family is Scottish, so I use other sites).
Did he have a son also called Henry Willard Harding? Born late 1884, died late 1896 or early 1897? :( Both of those entries show up too; both in Windsor, Surrey.
Henry Senior shows up in the National Probate Calendar, too.
I think there are various census entries as well.
You can get a free Ancestry membership for a week or two if you hand over card details; they are fine about cancelling it after the two weeks as long as you remember to ring up.
Good luck :)