Hi Pete
Take a look at this article from Search Engine Watch on how Google handles 410 codes.
In short, 404 means "page not found", while a 410 means "this page is gone and we do not expect it to come back". If this is in fact the circumstance - the page is gone, not coming back - then a 410 lets Google know that that is official, and you can now ignore this page.
A couple of things to note from the article from Matt Cutts...
"If we see a 410, then the site crawling system says, OK we assume the webmasters knows what they're doing because they went off the beaten path to deliberately say this page is gone," he said. "So they immediately convert that 410 to an error, rather than protecting it for 24 hours.
So when you do serve a 410 status code on a page that really isn't gone permanently, you haven't killed that page off permanently. Googlebot will return the check and see if the page needs to be returned to the index.
"Now don't take this too much the wrong way, we'll still go back and recheck and make sure are those pages really gone, or maybe the pages have come back alive again," Cutts said. "And I wouldn't rely on the assumption that that behavior will always be exactly the same.
"In general, sometimes webmasters get a little too caught up in the tiny little details and so if the page is gone, it's fine to serve a 404, if you know it's gone for real it's fine to serve a 410," he said. "But we'll design our crawling system to try and be robust so that if your site goes down, or if you get hacked, or whatever that we try to make sure that we can still find the good content whenever it's available." As far as why your 404s are appearing in your Webmaster Tools; I would check your internal links and make sure they are up to date, and also that your sitemap is up to date. If pages need to be redirected to more relevant pages, make sure those are doing so, otherwise, create a custom 404 page so that users can navigate or find what they need. 410s aren't usually necessary, so I would discuss with your SEO team their reasoning. Review what I passed over though!
Hope this helps, good luck!