£44 for the vet trip in Fulham, SW London!!
My dog had a corneal ulcer last year and it went on for weeks - I took him to the vet on day 2 and got him eye-drops. The symptoms were weepy, conjunctivits as well as a swollen inner third eye-lid and lots of squinting. I could see the ulcer too. It is apparently extremely painful for the dog.
For £14 I'd take him in for a check-up!
In the meantime, everyone's suggestion of cleaning it with luke-warm boiled water and a flat cotton pad are good. My vet said don't bother with salt, but make sure it's distilled (ie boiled and then cooled down a bit).