The issue of a clamp has been raised as a possible solution... From looking at it, I am not so certain that it works.
The outcome here is that White needs to win the Ko (two Ko fights when Black can draw back at b as well) to stay connected. There is one eye in the top left corner (unless Black plays to eliminate it) but with White crawling along the edge, eyes can be made false. And even if White can continue crawling, it may be possible for Black to eliminate White's eye on the left (and then chase the clump of false eye connections..
As you can see from this long sequence, careful reading is required to see if life is possible. I am unsure if my reading here is correct.
I have spent some time on this problem and think a rest is required before re-tackling it. Anyone wanting to ad their thoughts are most welcome. - Mystery Go Player?
Malcolm: What about this follow-up for White?
tderz: Much better then above.
Or, even earlier:
KendoKa? This is the solution I found... White can't tenuki on 3 and if black want's to kill at 7 neglecting 5 he will die in a ladder ;)