......anyone able to recommend anything available for free download, which isn't only a trial version?

Any assistance gratefully received

http://www.piriform.com/recuva

What he said, there are tonnes of "dedicated" programs to rescue photos etc from SD cards, but the Piriform software is MUCH better. While downloading it, consider getting their other programs as well, they are ALL GREAT.

I've used PhotoRec in the past as well, which had very good results (although mangled the filenames, so the order of pictures changed slightly).

I got a copy of RescuePro with a Sandisk card and that works OK. Not sure if It's free though.

If you've just deleted things by accident you should get everything back pretty easily.

If you've overwitten anything then you may be fooked.