Just reporting back that "Herman" cake turned out delicious - so if you are lucky enough to be given a portion of "starter", then give it a go. I dutifuly gave some portions away, but kept one to make another cake in another 10 days time.
The young man has a Christmas job at a local supermarket. He's on fruit and veg, and at the end of his shift marks down the prices. He made me laugh when in his break, he sent me a text that simply said "Cucumbers 2p" - that's my boy!
So I popped in and bought a job lot before I picked him up, and the grandparents will have a home made jar of Cucumber Pickle in their hampers for Christmas.