Thank you all for taking the time to reply.
The pages are long gone, replaced by a script that sends a 410 header and redirects visitors to a Page Gone notice. The sitemap doesn’t include them, nor do any pages on the site link to them. The pages in question do not show in serps either, just WMT, so not sure if the Remove URL tool would apply.
Comforting to hear not2easy say this can take a while. Google discover a fresh batch of 410s daily so it seems all we need apply is a little more patience.
Thanks again, you’ve put my mind at ease.