I have exactly the same problem with my Champion (R484) lawnmower. The lower handle has sheared from its attachment. I have looked for a website to buy the spare part but to no avail. There is a phone helpline (01889 566183) but it is not manned at the weekend. Another excuse not to cut the grass!
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix lawn mowers.