how can I fix a chip in double glazed window?

Chris - are you still looking for an answer for this? You might want to give these guys a try...
http://www.glasweld.info/scratch_index.html
I used them to repair scratches on my car passenger window, and they did a great job. Not sure about double glazing but, like you, have just discovered a couple of chips in our window so am considering giving them a call.

Alex
September 2009

Only by replacing the entire glass unit, Chris.

John
July 2009