Thanks everyone. I managed to sort it by rebuilding my iPhoto library - good old google showed me how. I'm feeling all smug because DH was telling me how the photos were lost and could not be recovered
Doh! Just seen reference to iPhoto. To run Recuva [http://www.piriform.com/recuva/download] you'll need to use a Windows PC (preferably one with a card reader slot, to directly insert your camera memory card.)
Try running Piriform's Recuva on the camera's memory card. If you've not saved any other pictures to the card between when they were deleted and now, they'll all still be there. The space they occupy is just marked as available for overwriting. The files are only truly gone when they are overwritten.
You can't recover full size photos from thumbnails.
The files might still be on the SD card but corrupted (you won't necessarily be able to see them) and might be restorable. There are all kinds of programs available online which you can use to recover corrupted photos, but I'm afraid I can't recommend one. Worth a Google though. Often they have free trials which allow you to recover a certain number of MBs before having to pay for the full version.
I'm having a huge disaster. I've just tried downloading my photos off my camera into iPhoto. The software crashed partway between downloading, deleting originals and finishing the import. These photos are not in my iPhoto library or on my camera. I have browsed my hard drive and found the thumbnails. Can I do anything to turn these back into full size photos or are they lost forever?
Have made mental note not to trust iPhoto to delete my originals again and will do it manually after import has been confirmed.