Hi Phil, Many thanks for your help. That worked a treat!
I should have explained that the 'junk' I mentioned was partly old keywords I had added with Adobe Photoshop Elements 4 and partly meta that the aforementioned application wrote to the files without my knowledge.
My goal is to tidy up 14000 images to be "as shot" so I can import them clean into Lightroom.I have found keywords writen into Exif, IPTC and XMP and I would prefer to null the IPTC and XMP and ensure the exif data is as I would like prior to Lightroom indexing the images. Does this seem sensible?