DESCRIPTION:
Update: Identified!

After posting this, I realized it might just work to email the organizers of the Greenwich Comedy Festival. And as a result, I can now happily report that the band in question are called The Wagon Tales.
http://www.wagontales.co.uk/
And they seem to have an EP available on Amazon/iTunes.
http://www.amazon.com/EP/dp/B006TGV1LG/

Previous Description:

Please help!

We saw this amazing bluegrass band at the 2011 Greenwich Comedy Festival (while waiting to see Tim Minchin), but we forgot their name.

Two more clips are available:
http://youtu.be/MD-irbEfKQI
http://youtu.be/zexZMsJhcUU

Please leave a comment if you know who these guys are.

Thanks!