There's a long thread on culturing the 1698 yeast here
http://www.thehomebrewforum.co.uk/showthread.php?t=60341
My experience, at least for the first generation, was that the yeast was so top fermenting that I had to keep turning the yeasty krausen into the brew to keep it going, since otherwise there was not enough actually in the liquid beer itself.
Interesting thread, thanks. Almost sounds like a yeast that would be suited to Yorkshire square, where the krausen would get washed back into the brew by the circulation of the wort. Might give the Fuller's yeast a go first to get my confidence up. I did successfully culture up Cooper's yeast a while back, but it didn't blow me away; I found it a bit neutral and didn't think it's added enough to justify the effort. Looking for something more fruity tits time.