The inner door handle should simply click into place by sliding over and behind the wedge shaped metal latch in the door frame. If it's not doing this it may need replacing.
You can get a spare from spares2go.co.uk for about £8 and it's pretty easy to replace, although a little bit fiddly - it requires a bit of force to get the handle clipped back on - make sure all four notches on the handle are aligned with the retaining pole on the door before trying to push into place.
Tom, December 2008
