Using pop Gmail on Modest isn't working for me either on N810 diablo, latest update installed. I Have exactly the same problem as Fionn: no error message or whatsoever. Even if I change the POP3 port number to an incorrect one, no error message shows up!
The Gmail account is working on my Windows PC without problems though...

By the way, other POP3 accounts I tried do work properly. So as a workaround, I let my gmail being forwarded to a "normal" pop3 account to be able to read my email on my N810.