Can you catch cold sores from glasses in pubs, if they have not been washed properly?

The question you ask is an interesting one. The short answer is no.
 
The root of a cold sore does not lie with what you are in contact with this week, this month or this year. For most, it goes back to childhood or the teenage years when the virus is picked up from an adult carrying the cold sore virus.
 
At the moment of infection, the typical cold sore does not appear and if any symptoms do arise, they resemble a mild cold.
 
These cold sore viruses are passed on without one knowing it - and unless  child is in the pub drinking from a poorly washed glass, it is unlikely that this will be the primary route of transmission.
 
Furthermore, after one picks up a cold sore virus, it takes years before cold sores actually develop.