Whereabouts in London will you be staying?

The Session is a very good resource, but it's always worth checking beforehand for the London sessions it lists. There are several defunct sessions listed I think, and also many sessions which are "3rd Thursday of the month" etc - so it is sometimes hard to know if a session is definitely on.

I'm afraid I'm more of an English player, but for what it's worth here are the London sessions I enjoy:

The River Ale House in Woolwich (Tuesdays): English tunes
The Dog & Bell in Deptford (Wednesdays): mix of English and Irish
No Frills Session at the Windmill pub in Brixton: mostly Irish tunes, but some English and American (2nd Sunday of every month)

I hear good things about the Irish session at the Harrison pub in Kings Cross. I've never been but I like the pub: good food. I think that one might also be 2nd Sunday of the month: check the Harrison's website.