Stuart, have installed the latest raw support update 4.08? That apparently introduced a bug, and removed the lens correction from the raw support for the Sony RX100. As a result the photos are showing a barrel distortion.
The fix is to uninstall 4.08 and to revert to the previous raw support.
See also the info on Apple's support site: Aperture 3.x: RAW files from Sony RX100 might appear distorted http://support.apple.com/kb/TS5192
Thank you so much for this guidance. It has worked successfully. I've been bugging Sony for weeks thinking that there was a problem with the camera. Guess I need to go apologise to them now
Thanks for replying so quickly, I'm now in the process of correcting the photos!
Have a great weekend.