Humm, might be dodgy? @McMullan should have a better answer. Hasn't been around here for a couple of months, but he lurks about Jim's so you might catch him there (take a mirror or you might miss him - contrary to some beliefs, he does have a reflection).I am currently in England for a few days and have the following (maybe stupid) question:
Is it possible to use good quality cask ale to start a yeast culture?
...
PS: It‘s the Harvey‘s yeast I am after…
Otherwise, you might try to avoid the uncertainty of coming back with a good sample and switch to the uncertainty of "is it Harvey's or isn't it?" and grab a Brewlabs "Sussex" yeast-slope. (Some think it is, some think it's no such thing). The Malt Miller (UK) sell it, but there's more than one; I think the Malt Miller do "Sussex 1"?