Toks - you need to be careful in banding around average speed statistics, even if the BCF seems to give them some kind of credence to similar figures on their Website.
I did not join a cycling club for years (around ten to be precise!) based on the misguided notion that there was no hope for you if you couldn't average 20mph. This view was perpetrated widely at the time, and of course 20mph was easy for all the club cyclists I knew! Annoyingly people (e.g. BCF) still use this as a benchmark.
Sorry - but IMHO it is a very unhelpful target. When racing on a flat time trial course for 10miles with no junctions to slow down for when you can maintain your pace, then evens (20mph) is a respectable target for a novice. However, newcomers to racing have never had this opportunity to test themselves. Further as flat-road TTing favours heavier adult riders rather than leaner junior ones, an average of 16-17mph around a reasonably tough circuit on your own is a more representative target. Had I know this 15 years ago, my cycling-life may have been very different!