One option you could try, if you haven't already tried it, would be to log off of eBay UK and log onto one of eBay's overseas websites instead. Whenever I've used this workaround solution to get around site glitches specific to eBay UK I've always used www.ebay.com, which is the American version of the site, and which I've always found to be very useful for successfully getting around eBay UK site glitches.
Once you've logged off of eBay UK and onto one of eBay's overseas websites try to delete the items that you no longer want on your Watch List. If the items in question appear to have been succesfully deleted when you try to do this then log out of the overseas website and log back into eBay UK to check that they really have disappeared. Hopefully the items should have vanished from your Watch List given that you deleted them earlier on, albeit via one of eBay's other websites and not eBay UK. It may not work, but you've got nothing to lose by trying it to see whether it does solve the problem.
