Suggestions please for re-fixing handle to hollow hardboard wardrobe
door (no lock-block).

The handle was fixed with a dowel screw (machine thread to wood
thread) like this:

http://www.screwfix.com/prods/17878/...0mm-Pack-of-10

but it's worked loose over the years.

I thought that putting a bolt right through the door from the back
would be an easy solution but the knob has an old imperial (?) thread
-- not sure what exactly but the pitch of the thread doesn't match
metric bolts.

So any other suggestions? A source of imperial (?) bolts that doesn't
involve buying a box of 100 (and how to identify the thread)? Some
sort of cavity fixing that would work on a single thickness of
hardboard? A solution that doesn't involve buying a whole new set of
matching handles would be good.

Thanks in advance.