Problem Solved
Thanks for all the able assistance but:
I appear to have fixed that problem by attributing (moving) the Temporary Internet Files Folder to a 250MB zip disk and then booting up without the disk in. It just put up an error message and then accepted a new zip disk with a folder of that name ("Temporary Internet Files"). The pesky files have now disappeared. Wonder if they were some sort of Back Orifice feature to give access? The longer one turned out to be a clickable link (but to nowhere of interest - just a Google search return page).
I can now delete the cache files without any hang-up.
But it makes me wonder whether Google are now into embedding a sleeper program or two.
Don't control your paranoia, savour it.