been using irc for about 4 years, never had no problems until roughly the 24th-25th of november this year (bt internet), tested on :

bt homehub
bt voyager
green frog modem (so i could see if it was any hardware firewall)
DLINK DSL504T

same problem on every one, as soon as i start a DCC send, or recieve, instant disconnect, no messages or anything for about 10 minutes, and then it eventually realises i have been disconnected.

if this helps : im in yorkshire (not sure if its a region thing) and my ip address is on the 86 range.