The session leaders both booked and fringe are generally happy for anyone to start up a tune when there is a lull. You go to a session where the expected norm is wall-to-wall Irish reels but there are plenty of opportunities to start up slower tunes and tunes from other places as often happens. As already stated the main problem is getting a seat or even getting in. Here the main remedy is get there early or wait around till someone leaves.

Personally I prefer music sessions as you can join in with most tunes, but when I went to the Station one evening to meet up with old friends all 3 singing sessions were full up, well established and not looking like anyone would be leaving. If you are new to Whitby I recommend you leave your instrument at home for the first couple of days and go on a pub crawl to see what happens in all of the pubs. Someone posted a list of all the pubs where it happens not so long back.