shameless plugging I knowfolk/acoustic guide for Londonish area at:
http://www.members.aol.com/folkandroots/index.html
Theres a couple of good concerts coming up at the Purcell room in the South bank centre this week, Slainte Mhath(Tuesday) from Cape Breton and Gjallarhorn on friday both sound well worth catching, Sliante Mhath are doing a freebie on Wednesday lunchtime outside the Oxo tower on South Bank (12:30 if memory recalls).