I made all my Christmas puds and Christmas cakes a couple of weeks ago. I ALWAYS steam the puds for 8 hours and then, when cool, put in a dark place, tightlty wrapped in an airtight container and 'feed' weekly with alcohol. On Christmas day I re-steam for about 2-2.5 hours, although some in my family don't re-steam, but cook in a microwave (not sure how long).
Maybe Rachel Allen's recipe is a 'light' version of the traditional pud? If so, then it might not need to be steamed for so long. I've only ever used my family recipe, but I have eaten a Delia Smith recipe pudding a few times, as a friend makes them to her recipe. She also steams it for 8 hours.
Until you find out whether it was a missed line, or a less rich, intense mixture, I'm not sure what to recommend. Is the mixture still sloppy and uncooked?