There is a site in the USA maintained by a man called Christopher Brennan. It lists all the singing sessions in Ireland and many in the USA. It's fairly well up to date and lists the sessions according to county. If you send him an email with details I'm sure he will start a section for the UK.
See
http://www.irishrochester.org/SINGERS%20WEB/singers2.htm

You may email Christopher at mailto:cristoir@optonline.net