There are a number of sessions in Luton which are often listed in the expat Irish newspapers, and there are numerous folk events in Hitchin...
BUT
Falling geographically between the two, and technically inferior to both is the Kings Walden Tuesday Sing-Along Session!
An informal handful of beginners, failures, wannabes, amateurs and the occasional competent musician get together at The Plough pub in Plough Lane, Ley Green, Kings Walden, Herts. Kick-off is usually around 8pm or 8.30pm every Tuesday.
The emphasis is on folk songs (mostly Irish, Scottish English and Australian with a couple of American standards thrown in for the sake of it.), with the occasional instrumental interlude. It is NOT a respectable ITM session, it is an excuse for a bunch of people to have fun and a couple of beers.
At the moment, most weeks have banjo, mandolin, whistle, concertina or melodeon or both, guitar, bodhran and a bunch of "singers" whose talent is only surpassed by... pretty much anything you care to nominate.
"Serious" musicians probably won't want to touch this mongrel with a ten-foot pole. On the other hand, the more relaxed breed of player may well love it.
There is space in the car park for your ego. However, please do NOT leave your sense of humour outside... you're going to need it.