I made the ESB Fresh Wort Bock last year, using the White Labs marzen/oktoberfest yeast. It actually said on the container to not add water if you wanted a "real" bock. I baulked at first, as this would only give me 15L of Bock, minus the volume left with the yeast cake, after 2 weeks of fermentation and 6 weeks of lagering, tieing up my fermenter all that time. However, i went ahead with it and it turned out to be a pretty special beer, malty, complex and true to style. Everyone loved it. I think in the end it was worth it, but it's such a shame that ESB can't make the wort that much higher in gravity, so I can add the 5L of water and still get a "real" bock.
Reg, your point is valid and ESB need to wake up to themselves.
Cheers - Snow.