Hello Simon,
Yes, Croydon Folksong Club is well worth a visit. (www.croydonfolksongclub.org.uk/)
There is also a session at The Wo Brewers on the 2nd Tuesday of the Month.
It is also worth trying the Bluegrass Plus Club, every 2nd Friday in the month (more details at www.bluegrass-plusclub.co.uk)
Best wishes,
Peter