Can someone confirm or deny for me that this is seki? The surrounding black stones can't be captured:

I am playing black and I have lost the game either way.

Nope, it's a special situation called bent four in the corner, so white is dead (or black can kill by ko at the end of the game).

http://senseis.xmp.net/?BentFourInTheCorner
http://senseis.xmp.net/?BentFourInTheCornerIsDead

The white stones are dead in a bent four. Look it up in SL - there is lots of information about it.

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Still officially AGA 5d but I play so irregularly these days that I am probably only 3d or 4d over the board (but hopefully still 5d in terms of knowledge, theory and the ability to contribute).

Ugh, this one still catches me out. Good job I wasn't the first one to see this thread.

OK. I see that there are good instructions for follow-through in the second link.

Thanks for the replies!