I had a good time visiting the Greenwich session two weeks running last month (Lord Hood pub, near Cutty Sark DLR station, every Tuesday, 9pm-11pm). Mainly English tunes: Scottish and Continental ok in small amounts. They have a tunebook collected from what they've played over the last 15 years or so, which is very well done (no accordion chords, though). http://www.greentrad.org.uk/ .