I can't offer much information pertaining to the Harding brand, but I can help a bit with identifying vintage. Apply some of the information offered in
How Old Is My Bike?, paying closest attention to
Component Numbers. That should get you pretty close to determining how old the bike is.
As for
Determining Bicycle Value, that is a whole different ball game and, generally, it is pretty difficult to predict how much a vintage bicycle is worth. Many things impact value, including location, time of year, size of bike and things like that.
Hope this is a bit of help and nice bike, by the way. I have had a few similar ones, including one still hanging in
The Old Shed.